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 $50.67   12.628%   $57.0686   $57.07   $57.05   $57.10  
  Purchase #2 $114.33   9.571%   $125.2725   $125.27   $125.25   $125.30  
  Purchase #3 $61.69   10.603%   $68.231   $68.23   $68.25   $68.20  
  Purchase #4 $241.99   10.146%   $266.5423   $266.54   $266.55   $266.50  
  Purchase #5 $69.94   8.179%   $75.6604   $75.66   $75.65   $75.70  
  Purchase #6 $243.78   4.409%   $254.5283   $254.53   $254.55   $254.50  
  Purchase #7 $187.83   9.351%   $205.394   $205.39   $205.40   $205.40  
  7 purchase totals = $970.23       $1,052.6971   $1,052.69   $1,052.70   $1,052.70