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 $67.55   8.810%   $73.5012   $73.50   $73.50   $73.50  
  Purchase #2 $122.37   9.455%   $133.9401   $133.94   $133.95   $133.90  
  Purchase #3 $173.77   7.424%   $186.6707   $186.67   $186.65   $186.70  
  Purchase #4 $125.96   13.742%   $143.2694   $143.27   $143.25   $143.30  
  Purchase #5 $12.44   4.867%   $13.0455   $13.05   $13.05   $13.00  
  Purchase #6 $90.48   4.277%   $94.3498   $94.35   $94.35   $94.30  
  Purchase #7 $130.65   8.395%   $141.6181   $141.62   $141.60   $141.60  
  7 purchase totals = $723.22       $786.3948   $786.40   $786.35   $786.30