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 $82.56   12.125%   $92.5704   $92.57   $92.55   $92.60  
  Purchase #2 $240.31   3.637%   $249.0501   $249.05   $249.05   $249.10  
  Purchase #3 $156.26   12.133%   $175.219   $175.22   $175.20   $175.20  
  Purchase #4 $52.72   3.181%   $54.397   $54.40   $54.40   $54.40  
  Purchase #5 $6.54   12.603%   $7.3642   $7.36   $7.35   $7.40  
  Purchase #6 $200.43   5.632%   $211.7182   $211.72   $211.70   $211.70  
  Purchase #7 $65.32   12.469%   $73.4648   $73.46   $73.45   $73.50  
  7 purchase totals = $804.14       $863.7837   $863.78   $863.70   $863.90