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 $249.53   6.611%   $266.0264   $266.03   $266.05   $266.00  
  Purchase #2 $249.35   9.426%   $272.8537   $272.85   $272.85   $272.90  
  Purchase #3 $96.70   4.324%   $100.8813   $100.88   $100.90   $100.90  
  Purchase #4 $233.64   4.543%   $244.2543   $244.25   $244.25   $244.30  
  Purchase #5 $230.61   6.241%   $245.0024   $245.00   $245.00   $245.00  
  Purchase #6 $213.42   7.591%   $229.6207   $229.62   $229.60   $229.60  
  Purchase #7 $94.42   5.551%   $99.6613   $99.66   $99.65   $99.70  
  7 purchase totals = $1,367.67       $1,458.3001   $1,458.29   $1,458.30   $1,458.40