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 $23.37   6.833%   $24.9669   $24.97   $24.95   $25.00  
  Purchase #2 $188.27   13.290%   $213.2911   $213.29   $213.30   $213.30  
  Purchase #3 $248.29   9.541%   $271.9793   $271.98   $272.00   $272.00  
  Purchase #4 $26.33   8.419%   $28.5467   $28.55   $28.55   $28.50  
  Purchase #5 $191.46   6.568%   $204.0351   $204.04   $204.05   $204.00  
  Purchase #6 $86.48   3.445%   $89.4592   $89.46   $89.45   $89.50  
  Purchase #7 $117.92   12.412%   $132.5562   $132.56   $132.55   $132.60  
  7 purchase totals = $882.12       $964.8345   $964.85   $964.85   $964.90