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 $124.62   7.653%   $134.1572   $134.16   $134.15   $134.20  
  Purchase #2 $169.36   11.589%   $188.9871   $188.99   $189.00   $189.00  
  Purchase #3 $180.49   11.785%   $201.7607   $201.76   $201.75   $201.80  
  Purchase #4 $15.84   13.236%   $17.9366   $17.94   $17.95   $17.90  
  Purchase #5 $96.47   7.858%   $104.0506   $104.05   $104.05   $104.10  
  Purchase #6 $113.46   4.383%   $118.433   $118.43   $118.45   $118.40  
  Purchase #7 $56.37   3.411%   $58.2928   $58.29   $58.30   $58.30  
  7 purchase totals = $756.61       $823.6180   $823.62   $823.65   $823.70