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 $246.73   3.362%   $255.0251   $255.03   $255.05   $255.00  
  Purchase #2 $20.29   11.366%   $22.5962   $22.60   $22.60   $22.60  
  Purchase #3 $87.58   10.168%   $96.4851   $96.49   $96.50   $96.50  
  Purchase #4 $141.80   13.675%   $161.1912   $161.19   $161.20   $161.20  
  Purchase #5 $185.76   9.282%   $203.0022   $203.00   $203.00   $203.00  
  Purchase #6 $142.35   6.703%   $151.8917   $151.89   $151.90   $151.90  
  Purchase #7 $125.40   4.236%   $130.7119   $130.71   $130.70   $130.70  
  7 purchase totals = $949.91       $1,020.9034   $1,020.91   $1,020.95   $1,020.90