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 $233.26   11.619%   $260.3625   $260.36   $260.35   $260.40  
  Purchase #2 $122.39   9.461%   $133.9693   $133.97   $133.95   $134.00  
  Purchase #3 $199.71   4.427%   $208.5512   $208.55   $208.55   $208.60  
  Purchase #4 $130.97   11.467%   $145.9883   $145.99   $146.00   $146.00  
  Purchase #5 $216.74   3.439%   $224.1937   $224.19   $224.20   $224.20  
  Purchase #6 $193.29   4.230%   $201.4662   $201.47   $201.45   $201.50  
  Purchase #7 $32.65   9.272%   $35.6773   $35.68   $35.70   $35.70  
  7 purchase totals = $1,129.01       $1,210.2085   $1,210.21   $1,210.20   $1,210.40