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 $229.64   11.756%   $256.6365   $256.64   $256.65   $256.60  
  Purchase #2 $142.36   13.545%   $161.6427   $161.64   $161.65   $161.60  
  Purchase #3 $241.88   10.205%   $266.5639   $266.56   $266.55   $266.60  
  Purchase #4 $54.43   4.632%   $56.9512   $56.95   $56.95   $57.00  
  Purchase #5 $141.41   8.302%   $153.1499   $153.15   $153.15   $153.10  
  Purchase #6 $197.88   8.213%   $214.1319   $214.13   $214.15   $214.10  
  Purchase #7 $208.50   7.658%   $224.4669   $224.47   $224.45   $224.50  
  7 purchase totals = $1,216.10       $1,333.5430   $1,333.54   $1,333.55   $1,333.50