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 $16.69   8.120%   $18.0452   $18.05   $18.05   $18.00  
  Purchase #2 $223.25   8.665%   $242.5946   $242.59   $242.60   $242.60  
  Purchase #3 $5.93   13.568%   $6.7346   $6.73   $6.75   $6.70  
  Purchase #4 $164.82   11.124%   $183.1546   $183.15   $183.15   $183.20  
  Purchase #5 $39.46   5.873%   $41.7775   $41.78   $41.80   $41.80  
  Purchase #6 $205.40   4.250%   $214.1295   $214.13   $214.15   $214.10  
  Purchase #7 $51.85   4.379%   $54.1205   $54.12   $54.10   $54.10  
  7 purchase totals = $707.40       $760.5565   $760.55   $760.60   $760.50