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 $60.34   6.682%   $64.3719   $64.37   $64.35   $64.40  
  Purchase #2 $196.42   9.367%   $214.8187   $214.82   $214.80   $214.80  
  Purchase #3 $70.57   6.571%   $75.2072   $75.21   $75.20   $75.20  
  Purchase #4 $153.25   11.725%   $171.2186   $171.22   $171.20   $171.20  
  Purchase #5 $112.61   4.132%   $117.263   $117.26   $117.25   $117.30  
  Purchase #6 $248.33   5.702%   $262.4898   $262.49   $262.50   $262.50  
  Purchase #7 $224.61   10.413%   $247.9986   $248.00   $248.00   $248.00  
  7 purchase totals = $1,066.13       $1,153.3678   $1,153.37   $1,153.30   $1,153.40