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 $246.35   8.464%   $267.2011   $267.20   $267.20   $267.20  
  Purchase #2 $13.92   4.593%   $14.5593   $14.56   $14.55   $14.60  
  Purchase #3 $200.60   13.555%   $227.7913   $227.79   $227.80   $227.80  
  Purchase #4 $215.44   4.401%   $224.9215   $224.92   $224.90   $224.90  
  Purchase #5 $124.57   10.401%   $137.5265   $137.53   $137.55   $137.50  
  Purchase #6 $184.96   5.359%   $194.872   $194.87   $194.85   $194.90  
  Purchase #7 $216.31   12.181%   $242.6587   $242.66   $242.65   $242.70  
  7 purchase totals = $1,202.15       $1,309.5304   $1,309.53   $1,309.50   $1,309.60