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 $234.62   13.807%   $267.014   $267.01   $267.00   $267.00  
  Purchase #2 $196.40   9.806%   $215.659   $215.66   $215.65   $215.70  
  Purchase #3 $160.86   3.710%   $166.8279   $166.83   $166.85   $166.80  
  Purchase #4 $233.55   3.722%   $242.2427   $242.24   $242.25   $242.20  
  Purchase #5 $68.34   10.591%   $75.5779   $75.58   $75.60   $75.60  
  Purchase #6 $18.32   5.301%   $19.2911   $19.29   $19.30   $19.30  
  Purchase #7 $96.28   4.598%   $100.707   $100.71   $100.70   $100.70  
  7 purchase totals = $1,008.37       $1,087.3196   $1,087.32   $1,087.35   $1,087.30