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 $33.51   9.326%   $36.6351   $36.64   $36.65   $36.60  
  Purchase #2 $170.44   12.252%   $191.3223   $191.32   $191.30   $191.30  
  Purchase #3 $106.35   10.235%   $117.2349   $117.23   $117.25   $117.20  
  Purchase #4 $182.98   7.647%   $196.9725   $196.97   $196.95   $197.00  
  Purchase #5 $48.96   7.357%   $52.562   $52.56   $52.55   $52.60  
  Purchase #6 $224.73   6.180%   $238.6183   $238.62   $238.60   $238.60  
  Purchase #7 $144.40   5.403%   $152.2019   $152.20   $152.20   $152.20  
  7 purchase totals = $911.37       $985.5470   $985.54   $985.50   $985.50