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 $213.49   7.321%   $229.1196   $229.12   $229.10   $229.10  
  Purchase #2 $59.75   10.353%   $65.9359   $65.94   $65.95   $65.90  
  Purchase #3 $93.99   11.379%   $104.6851   $104.69   $104.70   $104.70  
  Purchase #4 $174.43   13.359%   $197.7321   $197.73   $197.75   $197.70  
  Purchase #5 $74.94   10.352%   $82.6978   $82.70   $82.70   $82.70  
  Purchase #6 $45.40   9.521%   $49.7225   $49.72   $49.70   $49.70  
  Purchase #7 $60.69   8.713%   $65.9779   $65.98   $66.00   $66.00  
  7 purchase totals = $722.69       $795.8709   $795.88   $795.90   $795.80