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 $84.37   11.803%   $94.3282   $94.33   $94.35   $94.30  
  Purchase #2 $170.47   12.118%   $191.1276   $191.13   $191.15   $191.10  
  Purchase #3 $234.89   4.530%   $245.5305   $245.53   $245.55   $245.50  
  Purchase #4 $108.98   7.611%   $117.2745   $117.27   $117.25   $117.30  
  Purchase #5 $155.42   5.498%   $163.965   $163.97   $163.95   $164.00  
  Purchase #6 $185.64   6.752%   $198.1744   $198.17   $198.15   $198.20  
  Purchase #7 $44.99   11.235%   $50.0446   $50.04   $50.05   $50.00  
  7 purchase totals = $984.76       $1,060.4448   $1,060.44   $1,060.45   $1,060.40