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 $72.47   4.622%   $75.8196   $75.82   $75.80   $75.80  
  Purchase #2 $170.35   4.455%   $177.9391   $177.94   $177.95   $177.90  
  Purchase #3 $72.41   13.801%   $82.4033   $82.40   $82.40   $82.40  
  Purchase #4 $51.51   8.863%   $56.0753   $56.08   $56.10   $56.10  
  Purchase #5 $230.88   10.633%   $255.4295   $255.43   $255.45   $255.40  
  Purchase #6 $182.71   9.361%   $199.8135   $199.81   $199.80   $199.80  
  Purchase #7 $104.75   7.820%   $112.9415   $112.94   $112.95   $112.90  
  7 purchase totals = $885.08       $960.4218   $960.42   $960.45   $960.30