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 $22.47   9.640%   $24.6361   $24.64   $24.65   $24.60  
  Purchase #2 $158.70   11.334%   $176.6871   $176.69   $176.70   $176.70  
  Purchase #3 $83.55   5.667%   $88.2848   $88.28   $88.30   $88.30  
  Purchase #4 $89.36   6.247%   $94.9423   $94.94   $94.95   $94.90  
  Purchase #5 $62.94   5.565%   $66.4426   $66.44   $66.45   $66.40  
  Purchase #6 $184.81   7.361%   $198.4139   $198.41   $198.40   $198.40  
  Purchase #7 $198.73   5.658%   $209.9741   $209.97   $209.95   $210.00  
  7 purchase totals = $800.56       $859.3809   $859.37   $859.40   $859.30