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 $208.72   12.515%   $234.8413   $234.84   $234.85   $234.80  
  Purchase #2 $244.34   9.426%   $267.3715   $267.37   $267.35   $267.40  
  Purchase #3 $64.78   6.122%   $68.7458   $68.75   $68.75   $68.70  
  Purchase #4 $112.48   5.556%   $118.7294   $118.73   $118.75   $118.70  
  Purchase #5 $58.79   4.743%   $61.5784   $61.58   $61.60   $61.60  
  Purchase #6 $139.36   13.562%   $158.26   $158.26   $158.25   $158.30  
  Purchase #7 $79.35   8.759%   $86.3003   $86.30   $86.30   $86.30  
  7 purchase totals = $907.82       $995.8267   $995.83   $995.85   $995.80