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 $227.66   3.411%   $235.4255   $235.43   $235.45   $235.40  
  Purchase #2 $178.95   6.472%   $190.5316   $190.53   $190.55   $190.50  
  Purchase #3 $115.92   8.299%   $125.5402   $125.54   $125.55   $125.50  
  Purchase #4 $70.93   5.731%   $74.995   $75.00   $75.00   $75.00  
  Purchase #5 $232.84   7.510%   $250.3263   $250.33   $250.35   $250.30  
  Purchase #6 $166.43   13.262%   $188.5019   $188.50   $188.50   $188.50  
  Purchase #7 $185.63   5.396%   $195.6466   $195.65   $195.65   $195.60  
  7 purchase totals = $1,178.36       $1,260.9671   $1,260.98   $1,261.05   $1,260.80