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 $249.47   8.675%   $271.1115   $271.11   $271.10   $271.10  
  Purchase #2 $94.95   10.420%   $104.8438   $104.84   $104.85   $104.80  
  Purchase #3 $15.73   10.793%   $17.4277   $17.43   $17.45   $17.40  
  Purchase #4 $193.91   4.345%   $202.3354   $202.34   $202.35   $202.30  
  Purchase #5 $207.48   5.526%   $218.9453   $218.95   $218.95   $218.90  
  Purchase #6 $157.87   12.569%   $177.7127   $177.71   $177.70   $177.70  
  Purchase #7 $19.51   12.492%   $21.9472   $21.95   $21.95   $21.90  
  7 purchase totals = $938.92       $1,014.3236   $1,014.33   $1,014.35   $1,014.10