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 $203.62   11.320%   $226.6698   $226.67   $226.65   $226.70  
  Purchase #2 $13.53   6.240%   $14.3743   $14.37   $14.35   $14.40  
  Purchase #3 $164.26   5.399%   $173.1284   $173.13   $173.15   $173.10  
  Purchase #4 $97.56   6.786%   $104.1804   $104.18   $104.20   $104.20  
  Purchase #5 $82.33   12.763%   $92.8378   $92.84   $92.85   $92.80  
  Purchase #6 $64.65   13.462%   $73.3532   $73.35   $73.35   $73.40  
  Purchase #7 $45.47   13.276%   $51.5066   $51.51   $51.50   $51.50  
  7 purchase totals = $671.42       $736.0505   $736.05   $736.05   $736.10