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 $92.81   3.731%   $96.2727   $96.27   $96.25   $96.30  
  Purchase #2 $116.99   8.715%   $127.1857   $127.19   $127.20   $127.20  
  Purchase #3 $132.93   11.582%   $148.326   $148.33   $148.35   $148.30  
  Purchase #4 $56.47   3.534%   $58.4656   $58.47   $58.45   $58.50  
  Purchase #5 $102.81   9.134%   $112.2007   $112.20   $112.20   $112.20  
  Purchase #6 $125.52   9.603%   $137.5737   $137.57   $137.55   $137.60  
  Purchase #7 $228.98   13.825%   $260.6365   $260.64   $260.65   $260.60  
  7 purchase totals = $856.51       $940.6609   $940.67   $940.65   $940.70