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 $226.74   8.646%   $246.3439   $246.34   $246.35   $246.30  
  Purchase #2 $44.76   4.463%   $46.7576   $46.76   $46.75   $46.80  
  Purchase #3 $234.96   11.354%   $261.6374   $261.64   $261.65   $261.60  
  Purchase #4 $146.60   3.483%   $151.7061   $151.71   $151.70   $151.70  
  Purchase #5 $148.74   11.381%   $165.6681   $165.67   $165.65   $165.70  
  Purchase #6 $130.35   3.383%   $134.7597   $134.76   $134.75   $134.80  
  Purchase #7 $41.26   4.160%   $42.9764   $42.98   $43.00   $43.00  
  7 purchase totals = $973.41       $1,049.8492   $1,049.86   $1,049.85   $1,049.90