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 $84.47   9.253%   $92.286   $92.29   $92.30   $92.30  
  Purchase #2 $146.51   3.539%   $151.695   $151.70   $151.70   $151.70  
  Purchase #3 $81.58   8.725%   $88.6979   $88.70   $88.70   $88.70  
  Purchase #4 $159.87   4.423%   $166.9411   $166.94   $166.95   $166.90  
  Purchase #5 $174.77   12.320%   $196.3017   $196.30   $196.30   $196.30  
  Purchase #6 $241.31   3.314%   $249.307   $249.31   $249.30   $249.30  
  Purchase #7 $101.99   8.572%   $110.7326   $110.73   $110.75   $110.70  
  7 purchase totals = $990.50       $1,055.9613   $1,055.97   $1,056.00   $1,055.90