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 $83.57   3.558%   $86.5434   $86.54   $86.55   $86.50  
  Purchase #2 $197.99   8.213%   $214.2509   $214.25   $214.25   $214.30  
  Purchase #3 $220.66   6.490%   $234.9808   $234.98   $235.00   $235.00  
  Purchase #4 $51.42   7.814%   $55.438   $55.44   $55.45   $55.40  
  Purchase #5 $236.65   9.474%   $259.0702   $259.07   $259.05   $259.10  
  Purchase #6 $107.62   9.432%   $117.7707   $117.77   $117.75   $117.80  
  Purchase #7 $98.32   5.166%   $103.3992   $103.40   $103.40   $103.40  
  7 purchase totals = $996.23       $1,071.4532   $1,071.45   $1,071.45   $1,071.50