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 $204.75   13.555%   $232.5039   $232.50   $232.50   $232.50  
  Purchase #2 $73.38   9.778%   $80.5551   $80.56   $80.55   $80.60  
  Purchase #3 $68.85   10.731%   $76.2383   $76.24   $76.25   $76.20  
  Purchase #4 $119.30   4.838%   $125.0717   $125.07   $125.05   $125.10  
  Purchase #5 $157.68   6.328%   $167.658   $167.66   $167.65   $167.70  
  Purchase #6 $239.60   7.857%   $258.4254   $258.43   $258.45   $258.40  
  Purchase #7 $81.97   11.628%   $91.5015   $91.50   $91.50   $91.50  
  7 purchase totals = $945.53       $1,031.9539   $1,031.96   $1,031.95   $1,032.00