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 $163.33   6.150%   $173.3748   $173.37   $173.35   $173.40  
  Purchase #2 $230.58   8.191%   $249.4668   $249.47   $249.45   $249.50  
  Purchase #3 $195.89   4.447%   $204.6012   $204.60   $204.60   $204.60  
  Purchase #4 $100.77   7.436%   $108.2633   $108.26   $108.25   $108.30  
  Purchase #5 $154.42   3.166%   $159.3089   $159.31   $159.30   $159.30  
  Purchase #6 $63.60   5.456%   $67.07   $67.07   $67.05   $67.10  
  Purchase #7 $88.38   3.261%   $91.2621   $91.26   $91.25   $91.30  
  7 purchase totals = $996.97       $1,053.3471   $1,053.34   $1,053.25   $1,053.50