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 $206.69   12.633%   $232.8011   $232.80   $232.80   $232.80  
  Purchase #2 $45.97   8.440%   $49.8499   $49.85   $49.85   $49.80  
  Purchase #3 $158.92   10.185%   $175.106   $175.11   $175.10   $175.10  
  Purchase #4 $171.64   12.384%   $192.8959   $192.90   $192.90   $192.90  
  Purchase #5 $203.68   12.508%   $229.1563   $229.16   $229.15   $229.20  
  Purchase #6 $233.84   10.438%   $258.2482   $258.25   $258.25   $258.20  
  Purchase #7 $58.51   8.230%   $63.3254   $63.33   $63.35   $63.30  
  7 purchase totals = $1,079.25       $1,201.3828   $1,201.40   $1,201.40   $1,201.30