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 $63.47   9.306%   $69.3765   $69.38   $69.40   $69.40  
  Purchase #2 $153.35   4.103%   $159.642   $159.64   $159.65   $159.60  
  Purchase #3 $46.66   12.463%   $52.4752   $52.48   $52.50   $52.50  
  Purchase #4 $41.55   7.532%   $44.6795   $44.68   $44.70   $44.70  
  Purchase #5 $132.82   6.688%   $141.703   $141.70   $141.70   $141.70  
  Purchase #6 $221.70   9.358%   $242.4467   $242.45   $242.45   $242.40  
  Purchase #7 $137.42   8.576%   $149.2051   $149.21   $149.20   $149.20  
  7 purchase totals = $796.97       $859.5280   $859.54   $859.60   $859.50