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 $67.51   12.302%   $75.8151   $75.82   $75.80   $75.80  
  Purchase #2 $119.81   5.821%   $126.7841   $126.78   $126.80   $126.80  
  Purchase #3 $27.61   3.135%   $28.4756   $28.48   $28.50   $28.50  
  Purchase #4 $19.72   4.261%   $20.5603   $20.56   $20.55   $20.60  
  Purchase #5 $123.51   3.156%   $127.408   $127.41   $127.40   $127.40  
  Purchase #6 $131.30   3.368%   $135.7222   $135.72   $135.70   $135.70  
  Purchase #7 $189.87   8.378%   $205.7773   $205.78   $205.80   $205.80  
  7 purchase totals = $679.33       $720.5426   $720.55   $720.55   $720.60