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 $195.34   10.408%   $215.671   $215.67   $215.65   $215.70  
  Purchase #2 $59.49   3.777%   $61.7369   $61.74   $61.75   $61.70  
  Purchase #3 $118.75   3.519%   $122.9288   $122.93   $122.95   $122.90  
  Purchase #4 $247.81   4.849%   $259.8263   $259.83   $259.85   $259.80  
  Purchase #5 $104.77   11.278%   $116.586   $116.59   $116.60   $116.60  
  Purchase #6 $88.54   11.424%   $98.6548   $98.65   $98.65   $98.70  
  Purchase #7 $20.78   10.287%   $22.9176   $22.92   $22.90   $22.90  
  7 purchase totals = $835.48       $898.3214   $898.33   $898.35   $898.30