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 $105.43   13.458%   $119.6188   $119.62   $119.60   $119.60  
  Purchase #2 $186.25   7.679%   $200.5521   $200.55   $200.55   $200.60  
  Purchase #3 $233.82   4.644%   $244.6786   $244.68   $244.70   $244.70  
  Purchase #4 $46.56   9.548%   $51.0055   $51.01   $51.00   $51.00  
  Purchase #5 $85.90   12.762%   $96.8626   $96.86   $96.85   $96.90  
  Purchase #6 $156.79   10.267%   $172.8876   $172.89   $172.90   $172.90  
  Purchase #7 $79.86   5.241%   $84.0455   $84.05   $84.05   $84.00  
  7 purchase totals = $894.61       $969.6507   $969.66   $969.65   $969.70