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 $68.47   4.678%   $71.673   $71.67   $71.65   $71.70  
  Purchase #2 $152.54   3.496%   $157.8728   $157.87   $157.85   $157.90  
  Purchase #3 $60.51   7.606%   $65.1124   $65.11   $65.10   $65.10  
  Purchase #4 $85.77   3.411%   $88.6956   $88.70   $88.70   $88.70  
  Purchase #5 $72.54   3.403%   $75.0085   $75.01   $75.00   $75.00  
  Purchase #6 $47.93   9.789%   $52.6219   $52.62   $52.60   $52.60  
  Purchase #7 $126.26   10.114%   $139.0299   $139.03   $139.05   $139.00  
  7 purchase totals = $614.02       $650.0141   $650.01   $649.95   $650.00