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 $166.66   5.414%   $175.683   $175.68   $175.70   $175.70  
  Purchase #2 $104.83   12.123%   $117.5385   $117.54   $117.55   $117.50  
  Purchase #3 $183.39   4.819%   $192.2276   $192.23   $192.25   $192.20  
  Purchase #4 $140.55   4.407%   $146.744   $146.74   $146.75   $146.70  
  Purchase #5 $149.96   12.208%   $168.2671   $168.27   $168.25   $168.30  
  Purchase #6 $191.88   6.504%   $204.3599   $204.36   $204.35   $204.40  
  Purchase #7 $16.57   11.642%   $18.4991   $18.50   $18.50   $18.50  
  7 purchase totals = $953.84       $1,023.3192   $1,023.32   $1,023.35   $1,023.30