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 $234.95   8.254%   $254.3428   $254.34   $254.35   $254.30  
  Purchase #2 $50.91   13.641%   $57.8546   $57.85   $57.85   $57.90  
  Purchase #3 $110.79   4.826%   $116.1367   $116.14   $116.15   $116.10  
  Purchase #4 $84.53   10.332%   $93.2636   $93.26   $93.25   $93.30  
  Purchase #5 $64.55   13.255%   $73.1061   $73.11   $73.10   $73.10  
  Purchase #6 $125.49   13.118%   $141.9518   $141.95   $141.95   $142.00  
  Purchase #7 $205.69   11.164%   $228.6532   $228.65   $228.65   $228.70  
  7 purchase totals = $876.91       $965.3088   $965.30   $965.30   $965.40