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 $214.84   4.406%   $224.3059   $224.31   $224.30   $224.30  
  Purchase #2 $95.51   13.540%   $108.4421   $108.44   $108.45   $108.40  
  Purchase #3 $163.32   7.737%   $175.9561   $175.96   $175.95   $176.00  
  Purchase #4 $156.64   10.640%   $173.3065   $173.31   $173.30   $173.30  
  Purchase #5 $160.30   13.141%   $181.365   $181.37   $181.35   $181.40  
  Purchase #6 $182.99   11.833%   $204.6432   $204.64   $204.65   $204.60  
  Purchase #7 $125.68   11.793%   $140.5014   $140.50   $140.50   $140.50  
  7 purchase totals = $1,099.28       $1,208.5202   $1,208.53   $1,208.50   $1,208.50