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 $241.48   7.644%   $259.9387   $259.94   $259.95   $259.90  
  Purchase #2 $55.88   11.345%   $62.2196   $62.22   $62.20   $62.20  
  Purchase #3 $25.48   11.424%   $28.3908   $28.39   $28.40   $28.40  
  Purchase #4 $177.63   11.334%   $197.7626   $197.76   $197.75   $197.80  
  Purchase #5 $75.55   4.666%   $79.0752   $79.08   $79.10   $79.10  
  Purchase #6 $146.29   12.687%   $164.8498   $164.85   $164.85   $164.80  
  Purchase #7 $96.69   8.818%   $105.2161   $105.22   $105.20   $105.20  
  7 purchase totals = $819.00       $897.4528   $897.46   $897.45   $897.40