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 $65.39   10.108%   $71.9996   $72.00   $72.00   $72.00  
  Purchase #2 $56.26   8.821%   $61.2227   $61.22   $61.20   $61.20  
  Purchase #3 $200.96   12.597%   $226.2749   $226.27   $226.25   $226.30  
  Purchase #4 $188.44   8.299%   $204.0786   $204.08   $204.10   $204.10  
  Purchase #5 $189.72   3.113%   $195.626   $195.63   $195.65   $195.60  
  Purchase #6 $35.76   7.606%   $38.4799   $38.48   $38.50   $38.50  
  Purchase #7 $54.81   5.864%   $58.0241   $58.02   $58.00   $58.00  
  7 purchase totals = $791.34       $855.7058   $855.70   $855.70   $855.70