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 $244.72   3.785%   $253.9827   $253.98   $254.00   $254.00  
  Purchase #2 $60.91   4.693%   $63.7685   $63.77   $63.75   $63.80  
  Purchase #3 $205.61   8.589%   $223.2698   $223.27   $223.25   $223.30  
  Purchase #4 $238.69   11.220%   $265.471   $265.47   $265.45   $265.50  
  Purchase #5 $60.97   8.277%   $66.0165   $66.02   $66.00   $66.00  
  Purchase #6 $164.56   9.838%   $180.7494   $180.75   $180.75   $180.70  
  Purchase #7 $58.70   10.682%   $64.9703   $64.97   $64.95   $65.00  
  7 purchase totals = $1,034.16       $1,118.2282   $1,118.23   $1,118.15   $1,118.30