Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $202.62   11.459%   $225.8382   $225.84   $225.85   $225.80  
  Purchase #2 $109.35   12.212%   $122.7038   $122.70   $122.70   $122.70  
  Purchase #3 $238.85   11.331%   $265.9141   $265.91   $265.90   $265.90  
  Purchase #4 $156.34   11.437%   $174.2206   $174.22   $174.20   $174.20  
  Purchase #5 $108.84   5.844%   $115.2006   $115.20   $115.20   $115.20  
  Purchase #6 $146.93   6.415%   $156.3556   $156.36   $156.35   $156.40  
  Purchase #7 $237.94   4.869%   $249.5253   $249.53   $249.55   $249.50  
  7 purchase totals = $1,200.87       $1,309.7582   $1,309.76   $1,309.75   $1,309.70