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 $76.35   10.406%   $84.295   $84.30   $84.30   $84.30  
  Purchase #2 $119.85   4.586%   $125.3463   $125.35   $125.35   $125.30  
  Purchase #3 $104.66   7.315%   $112.3159   $112.32   $112.30   $112.30  
  Purchase #4 $138.56   6.494%   $147.5581   $147.56   $147.55   $147.60  
  Purchase #5 $88.47   3.479%   $91.5479   $91.55   $91.55   $91.50  
  Purchase #6 $202.93   4.348%   $211.7534   $211.75   $211.75   $211.80  
  Purchase #7 $29.26   11.237%   $32.5479   $32.55   $32.55   $32.50  
  7 purchase totals = $760.08       $805.3645   $805.38   $805.35   $805.30