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 $245.35   3.173%   $253.135   $253.14   $253.15   $253.10  
  Purchase #2 $131.57   11.703%   $146.9676   $146.97   $146.95   $147.00  
  Purchase #3 $202.47   10.852%   $224.442   $224.44   $224.45   $224.40  
  Purchase #4 $14.67   5.344%   $15.454   $15.45   $15.45   $15.50  
  Purchase #5 $235.44   4.616%   $246.3079   $246.31   $246.30   $246.30  
  Purchase #6 $22.41   9.674%   $24.5779   $24.58   $24.60   $24.60  
  Purchase #7 $244.77   4.737%   $256.3648   $256.36   $256.35   $256.40  
  7 purchase totals = $1,096.68       $1,167.2492   $1,167.25   $1,167.25   $1,167.30