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 $244.26   4.373%   $254.9415   $254.94   $254.95   $254.90  
  Purchase #2 $32.36   12.151%   $36.2921   $36.29   $36.30   $36.30  
  Purchase #3 $186.99   3.401%   $193.3495   $193.35   $193.35   $193.30  
  Purchase #4 $119.46   5.407%   $125.9192   $125.92   $125.90   $125.90  
  Purchase #5 $183.69   10.443%   $202.8727   $202.87   $202.85   $202.90  
  Purchase #6 $105.26   4.131%   $109.6083   $109.61   $109.60   $109.60  
  Purchase #7 $88.25   4.640%   $92.3448   $92.34   $92.35   $92.30  
  7 purchase totals = $960.27       $1,015.3281   $1,015.32   $1,015.30   $1,015.20