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 $65.56   11.409%   $73.0397   $73.04   $73.05   $73.00  
  Purchase #2 $157.93   8.636%   $171.5688   $171.57   $171.55   $171.60  
  Purchase #3 $101.92   13.211%   $115.3847   $115.38   $115.40   $115.40  
  Purchase #4 $246.25   9.546%   $269.757   $269.76   $269.75   $269.80  
  Purchase #5 $31.74   7.569%   $34.1424   $34.14   $34.15   $34.10  
  Purchase #6 $9.89   7.746%   $10.6561   $10.66   $10.65   $10.70  
  Purchase #7 $221.36   4.807%   $232.0008   $232.00   $232.00   $232.00  
  7 purchase totals = $834.65       $906.5495   $906.55   $906.55   $906.60