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 $54.46   10.828%   $60.3569   $60.36   $60.35   $60.40  
  Purchase #2 $227.62   13.737%   $258.8882   $258.89   $258.90   $258.90  
  Purchase #3 $214.25   5.142%   $225.2667   $225.27   $225.25   $225.30  
  Purchase #4 $120.61   4.461%   $125.9904   $125.99   $126.00   $126.00  
  Purchase #5 $48.52   11.506%   $54.1027   $54.10   $54.10   $54.10  
  Purchase #6 $195.73   11.406%   $218.055   $218.06   $218.05   $218.10  
  Purchase #7 $129.64   7.305%   $139.1102   $139.11   $139.10   $139.10  
  7 purchase totals = $990.83       $1,081.7701   $1,081.78   $1,081.75   $1,081.90