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 $197.45   3.112%   $203.5946   $203.59   $203.60   $203.60  
  Purchase #2 $128.81   11.192%   $143.2264   $143.23   $143.25   $143.20  
  Purchase #3 $143.76   13.472%   $163.1273   $163.13   $163.15   $163.10  
  Purchase #4 $104.82   10.571%   $115.9005   $115.90   $115.90   $115.90  
  Purchase #5 $49.56   3.771%   $51.4289   $51.43   $51.45   $51.40  
  Purchase #6 $183.27   7.816%   $197.5944   $197.59   $197.60   $197.60  
  Purchase #7 $44.54   7.537%   $47.897   $47.90   $47.90   $47.90  
  7 purchase totals = $852.21       $922.7691   $922.77   $922.85   $922.70