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 $217.73   3.773%   $225.945   $225.95   $225.95   $225.90  
  Purchase #2 $154.57   10.626%   $170.9946   $170.99   $171.00   $171.00  
  Purchase #3 $68.40   12.422%   $76.8966   $76.90   $76.90   $76.90  
  Purchase #4 $230.48   5.841%   $243.9423   $243.94   $243.95   $243.90  
  Purchase #5 $213.96   6.526%   $227.923   $227.92   $227.90   $227.90  
  Purchase #6 $70.45   5.683%   $74.4537   $74.45   $74.45   $74.50  
  Purchase #7 $161.67   11.432%   $180.1521   $180.15   $180.15   $180.20  
  7 purchase totals = $1,117.26       $1,200.3073   $1,200.30   $1,200.30   $1,200.30