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 $239.88   9.173%   $261.8842   $261.88   $261.90   $261.90  
  Purchase #2 $95.42   9.489%   $104.4744   $104.47   $104.45   $104.50  
  Purchase #3 $153.49   3.727%   $159.2106   $159.21   $159.20   $159.20  
  Purchase #4 $56.41   6.767%   $60.2273   $60.23   $60.25   $60.20  
  Purchase #5 $141.50   4.355%   $147.6623   $147.66   $147.65   $147.70  
  Purchase #6 $176.29   5.176%   $185.4148   $185.41   $185.40   $185.40  
  Purchase #7 $118.32   13.222%   $133.9643   $133.96   $133.95   $134.00  
  7 purchase totals = $981.31       $1,052.8379   $1,052.82   $1,052.80   $1,052.90