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 $28.33   3.177%   $29.23   $29.23   $29.25   $29.20  
  Purchase #2 $142.54   4.563%   $149.0441   $149.04   $149.05   $149.00  
  Purchase #3 $218.89   10.404%   $241.6633   $241.66   $241.65   $241.70  
  Purchase #4 $5.99   8.465%   $6.4971   $6.50   $6.50   $6.50  
  Purchase #5 $41.42   7.266%   $44.4296   $44.43   $44.45   $44.40  
  Purchase #6 $80.77   10.769%   $89.4681   $89.47   $89.45   $89.50  
  Purchase #7 $142.96   4.846%   $149.8878   $149.89   $149.90   $149.90  
  7 purchase totals = $660.90       $710.2200   $710.22   $710.25   $710.20