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 $242.99   8.108%   $262.6916   $262.69   $262.70   $262.70  
  Purchase #2 $169.54   9.345%   $185.3835   $185.38   $185.40   $185.40  
  Purchase #3 $154.71   8.626%   $168.0553   $168.06   $168.05   $168.10  
  Purchase #4 $72.33   11.731%   $80.815   $80.82   $80.80   $80.80  
  Purchase #5 $235.32   5.219%   $247.6014   $247.60   $247.60   $247.60  
  Purchase #6 $69.39   11.170%   $77.1409   $77.14   $77.15   $77.10  
  Purchase #7 $70.69   7.674%   $76.1148   $76.11   $76.10   $76.10  
  7 purchase totals = $1,014.97       $1,097.8025   $1,097.80   $1,097.80   $1,097.80