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 $233.42   5.796%   $246.949   $246.95   $246.95   $246.90  
  Purchase #2 $140.43   4.507%   $146.7592   $146.76   $146.75   $146.80  
  Purchase #3 $60.27   10.868%   $66.8201   $66.82   $66.80   $66.80  
  Purchase #4 $180.41   9.232%   $197.0655   $197.07   $197.05   $197.10  
  Purchase #5 $230.37   5.168%   $242.2755   $242.28   $242.30   $242.30  
  Purchase #6 $205.91   7.237%   $220.8117   $220.81   $220.80   $220.80  
  Purchase #7 $9.90   10.201%   $10.9099   $10.91   $10.90   $10.90  
  7 purchase totals = $1,060.71       $1,131.5909   $1,131.60   $1,131.55   $1,131.60