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 $107.27   5.821%   $113.5142   $113.51   $113.50   $113.50  
  Purchase #2 $170.69   13.164%   $193.1596   $193.16   $193.15   $193.20  
  Purchase #3 $162.49   4.708%   $170.14   $170.14   $170.15   $170.10  
  Purchase #4 $83.69   13.758%   $95.2041   $95.20   $95.20   $95.20  
  Purchase #5 $88.55   4.729%   $92.7375   $92.74   $92.75   $92.70  
  Purchase #6 $150.44   5.595%   $158.8571   $158.86   $158.85   $158.90  
  Purchase #7 $164.73   8.727%   $179.106   $179.11   $179.10   $179.10  
  7 purchase totals = $927.86       $1,002.7185   $1,002.72   $1,002.70   $1,002.70