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 $136.86   9.608%   $150.0095   $150.01   $150.00   $150.00  
  Purchase #2 $110.29   4.589%   $115.3512   $115.35   $115.35   $115.40  
  Purchase #3 $210.47   8.314%   $227.9685   $227.97   $227.95   $228.00  
  Purchase #4 $234.93   13.171%   $265.8726   $265.87   $265.85   $265.90  
  Purchase #5 $45.76   11.341%   $50.9496   $50.95   $50.95   $50.90  
  Purchase #6 $161.63   4.617%   $169.0925   $169.09   $169.10   $169.10  
  Purchase #7 $14.68   9.612%   $16.091   $16.09   $16.10   $16.10  
  7 purchase totals = $914.62       $995.3349   $995.33   $995.30   $995.40