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 $209.84   6.159%   $222.764   $222.76   $222.75   $222.80  
  Purchase #2 $215.75   12.442%   $242.5936   $242.59   $242.60   $242.60  
  Purchase #3 $8.82   11.627%   $9.8455   $9.85   $9.85   $9.80  
  Purchase #4 $195.59   13.620%   $222.2294   $222.23   $222.25   $222.20  
  Purchase #5 $175.63   9.293%   $191.9513   $191.95   $191.95   $192.00  
  Purchase #6 $99.36   9.679%   $108.9771   $108.98   $109.00   $109.00  
  Purchase #7 $74.64   13.648%   $84.8269   $84.83   $84.85   $84.80  
  7 purchase totals = $979.63       $1,083.1878   $1,083.19   $1,083.25   $1,083.20