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 $236.50   4.708%   $247.6344   $247.63   $247.65   $247.60  
  Purchase #2 $193.63   5.185%   $203.6697   $203.67   $203.65   $203.70  
  Purchase #3 $98.36   11.108%   $109.2858   $109.29   $109.30   $109.30  
  Purchase #4 $129.29   9.382%   $141.42   $141.42   $141.40   $141.40  
  Purchase #5 $124.82   8.134%   $134.9729   $134.97   $134.95   $135.00  
  Purchase #6 $16.80   10.655%   $18.59   $18.59   $18.60   $18.60  
  Purchase #7 $23.86   11.382%   $26.5757   $26.58   $26.60   $26.60  
  7 purchase totals = $823.26       $882.1485   $882.15   $882.15   $882.20