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 $60.97   6.269%   $64.7922   $64.79   $64.80   $64.80  
  Purchase #2 $54.72   7.754%   $58.963   $58.96   $58.95   $59.00  
  Purchase #3 $196.86   5.689%   $208.0594   $208.06   $208.05   $208.10  
  Purchase #4 $77.72   4.480%   $81.2019   $81.20   $81.20   $81.20  
  Purchase #5 $184.91   10.563%   $204.442   $204.44   $204.45   $204.40  
  Purchase #6 $25.35   13.144%   $28.682   $28.68   $28.70   $28.70  
  Purchase #7 $189.95   13.684%   $215.9428   $215.94   $215.95   $215.90  
  7 purchase totals = $790.48       $862.0833   $862.07   $862.10   $862.10