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 $119.88   6.788%   $128.0175   $128.02   $128.00   $128.00  
  Purchase #2 $239.25   11.557%   $266.9001   $266.90   $266.90   $266.90  
  Purchase #3 $53.31   12.609%   $60.0319   $60.03   $60.05   $60.00  
  Purchase #4 $59.62   10.645%   $65.9665   $65.97   $65.95   $66.00  
  Purchase #5 $64.49   10.597%   $71.324   $71.32   $71.30   $71.30  
  Purchase #6 $64.37   12.833%   $72.6306   $72.63   $72.65   $72.60  
  Purchase #7 $224.59   4.730%   $235.2131   $235.21   $235.20   $235.20  
  7 purchase totals = $825.51       $900.0837   $900.08   $900.05   $900.00