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 $86.72   5.622%   $91.5954   $91.60   $91.60   $91.60  
  Purchase #2 $175.89   13.459%   $199.563   $199.56   $199.55   $199.60  
  Purchase #3 $26.42   5.807%   $27.9542   $27.95   $27.95   $28.00  
  Purchase #4 $45.28   4.828%   $47.4661   $47.47   $47.45   $47.50  
  Purchase #5 $10.38   3.405%   $10.7334   $10.73   $10.75   $10.70  
  Purchase #6 $209.62   5.732%   $221.6354   $221.64   $221.65   $221.60  
  Purchase #7 $7.91   6.801%   $8.448   $8.45   $8.45   $8.40  
  7 purchase totals = $562.22       $607.3955   $607.40   $607.40   $607.40