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 $246.51   5.704%   $260.5709   $260.57   $260.55   $260.60  
  Purchase #2 $87.91   10.421%   $97.0711   $97.07   $97.05   $97.10  
  Purchase #3 $212.54   6.157%   $225.6261   $225.63   $225.65   $225.60  
  Purchase #4 $160.97   4.128%   $167.6148   $167.61   $167.60   $167.60  
  Purchase #5 $129.68   3.259%   $133.9063   $133.91   $133.90   $133.90  
  Purchase #6 $136.57   11.428%   $152.1772   $152.18   $152.20   $152.20  
  Purchase #7 $13.51   11.725%   $15.094   $15.09   $15.10   $15.10  
  7 purchase totals = $987.69       $1,052.0604   $1,052.06   $1,052.05   $1,052.10