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 $125.69   13.735%   $142.9535   $142.95   $142.95   $143.00  
  Purchase #2 $40.67   12.725%   $45.8453   $45.85   $45.85   $45.80  
  Purchase #3 $194.73   5.565%   $205.5667   $205.57   $205.55   $205.60  
  Purchase #4 $51.39   8.841%   $55.9334   $55.93   $55.95   $55.90  
  Purchase #5 $213.55   10.827%   $236.6711   $236.67   $236.65   $236.70  
  Purchase #6 $55.51   6.291%   $59.0021   $59.00   $59.00   $59.00  
  Purchase #7 $78.84   7.808%   $84.9958   $85.00   $85.00   $85.00  
  7 purchase totals = $760.38       $830.9679   $830.97   $830.95   $831.00