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 $60.34   12.638%   $67.9658   $67.97   $67.95   $68.00  
  Purchase #2 $186.46   12.728%   $210.1926   $210.19   $210.20   $210.20  
  Purchase #3 $173.27   4.689%   $181.3946   $181.39   $181.40   $181.40  
  Purchase #4 $46.35   12.188%   $51.9991   $52.00   $52.00   $52.00  
  Purchase #5 $17.98   5.103%   $18.8975   $18.90   $18.90   $18.90  
  Purchase #6 $163.92   3.110%   $169.0179   $169.02   $169.00   $169.00  
  Purchase #7 $110.82   3.540%   $114.743   $114.74   $114.75   $114.70  
  7 purchase totals = $759.14       $814.2105   $814.21   $814.20   $814.20