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 $95.73   5.512%   $101.0066   $101.01   $101.00   $101.00  
  Purchase #2 $235.92   11.833%   $263.8364   $263.84   $263.85   $263.80  
  Purchase #3 $200.72   7.422%   $215.6174   $215.62   $215.60   $215.60  
  Purchase #4 $140.80   5.140%   $148.0371   $148.04   $148.05   $148.00  
  Purchase #5 $49.89   4.152%   $51.9614   $51.96   $51.95   $52.00  
  Purchase #6 $101.45   8.769%   $110.3462   $110.35   $110.35   $110.30  
  Purchase #7 $92.57   13.350%   $104.9281   $104.93   $104.95   $104.90  
  7 purchase totals = $917.08       $995.7332   $995.75   $995.75   $995.60