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 $246.38   8.388%   $267.0464   $267.05   $267.05   $267.00  
  Purchase #2 $106.36   12.814%   $119.989   $119.99   $120.00   $120.00  
  Purchase #3 $31.35   4.849%   $32.8702   $32.87   $32.85   $32.90  
  Purchase #4 $127.31   11.288%   $141.6808   $141.68   $141.70   $141.70  
  Purchase #5 $176.72   9.394%   $193.3211   $193.32   $193.30   $193.30  
  Purchase #6 $214.41   12.165%   $240.493   $240.49   $240.50   $240.50  
  Purchase #7 $40.90   13.309%   $46.3434   $46.34   $46.35   $46.30  
  7 purchase totals = $943.43       $1,041.7439   $1,041.74   $1,041.75   $1,041.70