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 $108.60   8.316%   $117.6312   $117.63   $117.65   $117.60  
  Purchase #2 $205.33   13.161%   $232.3535   $232.35   $232.35   $232.40  
  Purchase #3 $169.38   3.523%   $175.3473   $175.35   $175.35   $175.30  
  Purchase #4 $142.45   9.519%   $156.0098   $156.01   $156.00   $156.00  
  Purchase #5 $97.91   9.534%   $107.2447   $107.24   $107.25   $107.20  
  Purchase #6 $60.40   9.314%   $66.0257   $66.03   $66.05   $66.00  
  Purchase #7 $113.62   7.130%   $121.7211   $121.72   $121.70   $121.70  
  7 purchase totals = $897.69       $976.3333   $976.33   $976.35   $976.20