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 $242.92   10.623%   $268.7254   $268.73   $268.75   $268.70  
  Purchase #2 $146.56   3.768%   $152.0824   $152.08   $152.10   $152.10  
  Purchase #3 $68.76   7.802%   $74.1247   $74.12   $74.10   $74.10  
  Purchase #4 $107.81   11.194%   $119.8783   $119.88   $119.90   $119.90  
  Purchase #5 $153.95   13.104%   $174.1236   $174.12   $174.10   $174.10  
  Purchase #6 $112.81   5.351%   $118.8465   $118.85   $118.85   $118.80  
  Purchase #7 $195.38   8.549%   $212.083   $212.08   $212.10   $212.10  
  7 purchase totals = $1,028.19       $1,119.8639   $1,119.86   $1,119.90   $1,119.80