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 $213.97   5.802%   $226.3845   $226.38   $226.40   $226.40  
  Purchase #2 $34.67   13.204%   $39.2478   $39.25   $39.25   $39.20  
  Purchase #3 $128.53   10.341%   $141.8213   $141.82   $141.80   $141.80  
  Purchase #4 $94.99   6.226%   $100.9041   $100.90   $100.90   $100.90  
  Purchase #5 $183.33   10.507%   $202.5925   $202.59   $202.60   $202.60  
  Purchase #6 $242.96   13.116%   $274.8266   $274.83   $274.85   $274.80  
  Purchase #7 $61.50   12.359%   $69.1008   $69.10   $69.10   $69.10  
  7 purchase totals = $959.95       $1,054.8776   $1,054.87   $1,054.90   $1,054.80