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 $41.62   8.522%   $45.1669   $45.17   $45.15   $45.20  
  Purchase #2 $58.88   9.525%   $64.4883   $64.49   $64.50   $64.50  
  Purchase #3 $247.43   10.326%   $272.9796   $272.98   $273.00   $273.00  
  Purchase #4 $33.26   8.142%   $35.968   $35.97   $35.95   $36.00  
  Purchase #5 $135.92   7.411%   $145.993   $145.99   $146.00   $146.00  
  Purchase #6 $23.30   8.162%   $25.2017   $25.20   $25.20   $25.20  
  Purchase #7 $153.74   11.767%   $171.8306   $171.83   $171.85   $171.80  
  7 purchase totals = $694.15       $761.6281   $761.63   $761.65   $761.70