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 $34.46   6.131%   $36.5727   $36.57   $36.55   $36.60  
  Purchase #2 $41.72   3.793%   $43.3024   $43.30   $43.30   $43.30  
  Purchase #3 $17.55   7.862%   $18.9298   $18.93   $18.95   $18.90  
  Purchase #4 $12.67   5.848%   $13.4109   $13.41   $13.40   $13.40  
  Purchase #5 $64.35   4.224%   $67.0681   $67.07   $67.05   $67.10  
  Purchase #6 $59.99   8.263%   $64.947   $64.95   $64.95   $64.90  
  Purchase #7 $210.99   11.279%   $234.7876   $234.79   $234.80   $234.80  
  7 purchase totals = $441.73       $479.0185   $479.02   $479.00   $479.00