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 $55.88   5.234%   $58.8048   $58.80   $58.80   $58.80  
  Purchase #2 $101.34   12.840%   $114.3521   $114.35   $114.35   $114.40  
  Purchase #3 $109.37   9.622%   $119.8936   $119.89   $119.90   $119.90  
  Purchase #4 $171.45   9.405%   $187.5749   $187.57   $187.55   $187.60  
  Purchase #5 $151.66   8.689%   $164.8377   $164.84   $164.85   $164.80  
  Purchase #6 $73.73   3.247%   $76.124   $76.12   $76.10   $76.10  
  Purchase #7 $161.75   3.440%   $167.3142   $167.31   $167.30   $167.30  
  7 purchase totals = $825.18       $888.9013   $888.88   $888.85   $888.90