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 $227.88   8.458%   $247.1541   $247.15   $247.15   $247.20  
  Purchase #2 $242.53   11.715%   $270.9424   $270.94   $270.95   $270.90  
  Purchase #3 $6.50   5.526%   $6.8592   $6.86   $6.85   $6.90  
  Purchase #4 $43.37   8.720%   $47.1519   $47.15   $47.15   $47.20  
  Purchase #5 $58.25   6.601%   $62.0951   $62.10   $62.10   $62.10  
  Purchase #6 $213.83   5.541%   $225.6783   $225.68   $225.70   $225.70  
  Purchase #7 $140.96   8.196%   $152.5131   $152.51   $152.50   $152.50  
  7 purchase totals = $933.32       $1,012.3941   $1,012.39   $1,012.40   $1,012.50