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 $164.64   13.422%   $186.738   $186.74   $186.75   $186.70  
  Purchase #2 $132.92   9.827%   $145.982   $145.98   $146.00   $146.00  
  Purchase #3 $211.46   4.835%   $221.6841   $221.68   $221.70   $221.70  
  Purchase #4 $127.89   11.579%   $142.6984   $142.70   $142.70   $142.70  
  Purchase #5 $223.73   9.163%   $244.2304   $244.23   $244.25   $244.20  
  Purchase #6 $44.66   4.420%   $46.634   $46.63   $46.65   $46.60  
  Purchase #7 $105.95   6.294%   $112.6185   $112.62   $112.60   $112.60  
  7 purchase totals = $1,011.25       $1,100.5854   $1,100.58   $1,100.65   $1,100.50