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 $182.42   4.842%   $191.2528   $191.25   $191.25   $191.30  
  Purchase #2 $67.51   7.459%   $72.5456   $72.55   $72.55   $72.50  
  Purchase #3 $201.97   12.488%   $227.192   $227.19   $227.20   $227.20  
  Purchase #4 $160.80   10.828%   $178.2114   $178.21   $178.20   $178.20  
  Purchase #5 $59.65   6.737%   $63.6686   $63.67   $63.65   $63.70  
  Purchase #6 $229.98   3.313%   $237.5992   $237.60   $237.60   $237.60  
  Purchase #7 $51.56   5.278%   $54.2813   $54.28   $54.30   $54.30  
  7 purchase totals = $953.89       $1,024.7509   $1,024.75   $1,024.75   $1,024.80