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 $92.48   6.213%   $98.2258   $98.23   $98.25   $98.20  
  Purchase #2 $249.35   8.473%   $270.4774   $270.48   $270.50   $270.50  
  Purchase #3 $236.34   10.846%   $261.9734   $261.97   $261.95   $262.00  
  Purchase #4 $155.57   9.351%   $170.1174   $170.12   $170.10   $170.10  
  Purchase #5 $177.51   4.698%   $185.8494   $185.85   $185.85   $185.80  
  Purchase #6 $46.28   3.133%   $47.73   $47.73   $47.75   $47.70  
  Purchase #7 $131.29   11.736%   $146.6982   $146.70   $146.70   $146.70  
  7 purchase totals = $1,088.82       $1,181.0716   $1,181.08   $1,181.10   $1,181.00