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 $96.98   13.178%   $109.76   $109.76   $109.75   $109.80  
  Purchase #2 $207.99   8.646%   $225.9728   $225.97   $225.95   $226.00  
  Purchase #3 $231.77   5.684%   $244.9438   $244.94   $244.95   $244.90  
  Purchase #4 $239.34   12.632%   $269.5734   $269.57   $269.55   $269.60  
  Purchase #5 $227.57   10.155%   $250.6797   $250.68   $250.70   $250.70  
  Purchase #6 $98.54   5.489%   $103.9489   $103.95   $103.95   $103.90  
  Purchase #7 $241.27   10.618%   $266.888   $266.89   $266.90   $266.90  
  7 purchase totals = $1,343.46       $1,471.7666   $1,471.76   $1,471.75   $1,471.80