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 $168.48   10.813%   $186.6977   $186.70   $186.70   $186.70  
  Purchase #2 $234.51   13.275%   $265.6412   $265.64   $265.65   $265.60  
  Purchase #3 $85.68   4.181%   $89.2623   $89.26   $89.25   $89.30  
  Purchase #4 $190.70   8.422%   $206.7608   $206.76   $206.75   $206.80  
  Purchase #5 $203.51   11.207%   $226.3174   $226.32   $226.30   $226.30  
  Purchase #6 $136.84   10.222%   $150.8278   $150.83   $150.85   $150.80  
  Purchase #7 $198.91   9.518%   $217.8423   $217.84   $217.85   $217.80  
  7 purchase totals = $1,218.63       $1,343.3495   $1,343.35   $1,343.35   $1,343.30