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 $208.83   5.744%   $220.8252   $220.83   $220.85   $220.80  
  Purchase #2 $159.77   9.472%   $174.9034   $174.90   $174.90   $174.90  
  Purchase #3 $73.92   3.176%   $76.2677   $76.27   $76.25   $76.30  
  Purchase #4 $36.92   12.866%   $41.6701   $41.67   $41.65   $41.70  
  Purchase #5 $6.87   7.472%   $7.3833   $7.38   $7.40   $7.40  
  Purchase #6 $39.48   3.142%   $40.7205   $40.72   $40.70   $40.70  
  Purchase #7 $175.66   13.649%   $199.6358   $199.64   $199.65   $199.60  
  7 purchase totals = $701.45       $761.4060   $761.41   $761.40   $761.40