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 $64.81   5.863%   $68.6098   $68.61   $68.60   $68.60  
  Purchase #2 $192.86   9.645%   $211.4613   $211.46   $211.45   $211.50  
  Purchase #3 $237.91   13.227%   $269.3784   $269.38   $269.40   $269.40  
  Purchase #4 $116.34   11.193%   $129.3619   $129.36   $129.35   $129.40  
  Purchase #5 $231.64   5.798%   $245.0705   $245.07   $245.05   $245.10  
  Purchase #6 $82.61   3.305%   $85.3403   $85.34   $85.35   $85.30  
  Purchase #7 $246.92   11.830%   $276.1306   $276.13   $276.15   $276.10  
  7 purchase totals = $1,173.09       $1,285.3528   $1,285.35   $1,285.35   $1,285.40