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 $181.87   12.593%   $204.7729   $204.77   $204.75   $204.80  
  Purchase #2 $107.70   10.727%   $119.253   $119.25   $119.25   $119.30  
  Purchase #3 $236.88   9.116%   $258.474   $258.47   $258.45   $258.50  
  Purchase #4 $29.82   12.741%   $33.6194   $33.62   $33.60   $33.60  
  Purchase #5 $167.56   10.339%   $184.884   $184.88   $184.90   $184.90  
  Purchase #6 $40.26   7.295%   $43.197   $43.20   $43.20   $43.20  
  Purchase #7 $207.30   10.601%   $229.2759   $229.28   $229.30   $229.30  
  7 purchase totals = $971.39       $1,073.4762   $1,073.47   $1,073.45   $1,073.60