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 $24.67   11.580%   $27.5268   $27.53   $27.55   $27.50  
  Purchase #2 $177.93   3.600%   $184.3355   $184.34   $184.35   $184.30  
  Purchase #3 $51.37   9.365%   $56.1808   $56.18   $56.20   $56.20  
  Purchase #4 $48.71   3.369%   $50.351   $50.35   $50.35   $50.40  
  Purchase #5 $195.74   11.316%   $217.8899   $217.89   $217.90   $217.90  
  Purchase #6 $159.33   5.566%   $168.1983   $168.20   $168.20   $168.20  
  Purchase #7 $237.61   13.255%   $269.1052   $269.11   $269.10   $269.10  
  7 purchase totals = $895.36       $973.5875   $973.60   $973.65   $973.60