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 $88.63   7.541%   $95.3136   $95.31   $95.30   $95.30  
  Purchase #2 $244.83   5.102%   $257.3212   $257.32   $257.30   $257.30  
  Purchase #3 $108.67   4.253%   $113.2917   $113.29   $113.30   $113.30  
  Purchase #4 $155.34   12.155%   $174.2216   $174.22   $174.20   $174.20  
  Purchase #5 $249.37   4.474%   $260.5268   $260.53   $260.55   $260.50  
  Purchase #6 $117.25   7.213%   $125.7072   $125.71   $125.70   $125.70  
  Purchase #7 $221.97   3.117%   $228.8888   $228.89   $228.90   $228.90  
  7 purchase totals = $1,186.06       $1,255.2709   $1,255.27   $1,255.25   $1,255.20