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 $250.97   10.181%   $276.5213   $276.52   $276.50   $276.50  
  Purchase #2 $8.99   12.521%   $10.1156   $10.12   $10.10   $10.10  
  Purchase #3 $162.83   7.583%   $175.1774   $175.18   $175.20   $175.20  
  Purchase #4 $214.26   8.348%   $232.1464   $232.15   $232.15   $232.10  
  Purchase #5 $48.93   9.674%   $53.6635   $53.66   $53.65   $53.70  
  Purchase #6 $82.83   9.665%   $90.8355   $90.84   $90.85   $90.80  
  Purchase #7 $195.86   5.491%   $206.6147   $206.61   $206.60   $206.60  
  7 purchase totals = $964.67       $1,045.0744   $1,045.08   $1,045.05   $1,045.00