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 $86.63   11.681%   $96.7493   $96.75   $96.75   $96.70  
  Purchase #2 $75.68   5.510%   $79.85   $79.85   $79.85   $79.90  
  Purchase #3 $228.81   3.424%   $236.6445   $236.64   $236.65   $236.60  
  Purchase #4 $98.45   12.580%   $110.835   $110.84   $110.85   $110.80  
  Purchase #5 $149.30   5.125%   $156.9516   $156.95   $156.95   $157.00  
  Purchase #6 $125.57   12.512%   $141.2813   $141.28   $141.30   $141.30  
  Purchase #7 $59.93   3.481%   $62.0162   $62.02   $62.00   $62.00  
  7 purchase totals = $824.37       $884.3279   $884.33   $884.35   $884.30