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 $200.94   3.844%   $208.6641   $208.66   $208.65   $208.70  
  Purchase #2 $47.30   11.224%   $52.609   $52.61   $52.60   $52.60  
  Purchase #3 $96.25   8.800%   $104.72   $104.72   $104.70   $104.70  
  Purchase #4 $153.68   8.635%   $166.9503   $166.95   $166.95   $167.00  
  Purchase #5 $169.87   10.706%   $188.0563   $188.06   $188.05   $188.10  
  Purchase #6 $6.39   3.573%   $6.6183   $6.62   $6.60   $6.60  
  Purchase #7 $9.42   7.480%   $10.1246   $10.12   $10.10   $10.10  
  7 purchase totals = $683.85       $737.7426   $737.74   $737.65   $737.80