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 $194.82   11.832%   $217.8711   $217.87   $217.85   $217.90  
  Purchase #2 $141.61   8.419%   $153.5321   $153.53   $153.55   $153.50  
  Purchase #3 $141.94   10.865%   $157.3618   $157.36   $157.35   $157.40  
  Purchase #4 $230.63   5.281%   $242.8096   $242.81   $242.80   $242.80  
  Purchase #5 $6.58   10.360%   $7.2617   $7.26   $7.25   $7.30  
  Purchase #6 $248.26   11.374%   $276.4971   $276.50   $276.50   $276.50  
  Purchase #7 $67.77   6.528%   $72.194   $72.19   $72.20   $72.20  
  7 purchase totals = $1,031.61       $1,127.5274   $1,127.52   $1,127.50   $1,127.60