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 $65.85   5.128%   $69.2268   $69.23   $69.25   $69.20  
  Purchase #2 $183.51   5.694%   $193.9591   $193.96   $193.95   $194.00  
  Purchase #3 $50.75   11.840%   $56.7588   $56.76   $56.75   $56.80  
  Purchase #4 $94.49   8.346%   $102.3761   $102.38   $102.40   $102.40  
  Purchase #5 $125.26   4.215%   $130.5397   $130.54   $130.55   $130.50  
  Purchase #6 $38.76   6.726%   $41.367   $41.37   $41.35   $41.40  
  Purchase #7 $148.88   9.554%   $163.104   $163.10   $163.10   $163.10  
  7 purchase totals = $707.50       $757.3315   $757.34   $757.35   $757.40