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 $167.76   8.697%   $182.3501   $182.35   $182.35   $182.40  
  Purchase #2 $63.27   12.350%   $71.0838   $71.08   $71.10   $71.10  
  Purchase #3 $8.38   9.216%   $9.1523   $9.15   $9.15   $9.20  
  Purchase #4 $18.67   5.610%   $19.7174   $19.72   $19.70   $19.70  
  Purchase #5 $216.49   12.827%   $244.2592   $244.26   $244.25   $244.30  
  Purchase #6 $76.80   13.693%   $87.3162   $87.32   $87.30   $87.30  
  Purchase #7 $178.84   5.137%   $188.027   $188.03   $188.05   $188.00  
  7 purchase totals = $730.21       $801.9060   $801.91   $801.90   $802.00