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 $227.57   8.556%   $247.0409   $247.04   $247.05   $247.00  
  Purchase #2 $213.54   11.710%   $238.5455   $238.55   $238.55   $238.50  
  Purchase #3 $244.69   9.509%   $267.9576   $267.96   $267.95   $268.00  
  Purchase #4 $217.88   8.260%   $235.8769   $235.88   $235.90   $235.90  
  Purchase #5 $213.65   3.608%   $221.3585   $221.36   $221.35   $221.40  
  Purchase #6 $141.67   6.689%   $151.1463   $151.15   $151.15   $151.10  
  Purchase #7 $8.71   8.792%   $9.4758   $9.48   $9.50   $9.50  
  7 purchase totals = $1,267.71       $1,371.4015   $1,371.42   $1,371.45   $1,371.40