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 $33.73   3.447%   $34.8927   $34.89   $34.90   $34.90  
  Purchase #2 $157.47   4.460%   $164.4932   $164.49   $164.50   $164.50  
  Purchase #3 $206.84   5.848%   $218.936   $218.94   $218.95   $218.90  
  Purchase #4 $96.31   5.465%   $101.5733   $101.57   $101.55   $101.60  
  Purchase #5 $241.31   7.339%   $259.0197   $259.02   $259.00   $259.00  
  Purchase #6 $31.28   5.477%   $32.9932   $32.99   $33.00   $33.00  
  Purchase #7 $95.41   7.844%   $102.894   $102.89   $102.90   $102.90  
  7 purchase totals = $862.35       $914.8021   $914.79   $914.80   $914.80