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 $245.81   7.463%   $264.1548   $264.15   $264.15   $264.20  
  Purchase #2 $201.71   3.487%   $208.7436   $208.74   $208.75   $208.70  
  Purchase #3 $116.27   11.436%   $129.5666   $129.57   $129.55   $129.60  
  Purchase #4 $77.39   11.858%   $86.5669   $86.57   $86.55   $86.60  
  Purchase #5 $41.76   12.677%   $47.0539   $47.05   $47.05   $47.10  
  Purchase #6 $84.88   5.445%   $89.5017   $89.50   $89.50   $89.50  
  Purchase #7 $184.29   8.274%   $199.5382   $199.54   $199.55   $199.50  
  7 purchase totals = $952.11       $1,025.1257   $1,025.12   $1,025.10   $1,025.20