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 $199.87   9.568%   $218.9936   $218.99   $219.00   $219.00  
  Purchase #2 $206.66   13.850%   $235.2824   $235.28   $235.30   $235.30  
  Purchase #3 $217.97   10.245%   $240.301   $240.30   $240.30   $240.30  
  Purchase #4 $176.48   5.369%   $185.9552   $185.96   $185.95   $186.00  
  Purchase #5 $41.42   12.477%   $46.588   $46.59   $46.60   $46.60  
  Purchase #6 $59.58   9.623%   $65.3134   $65.31   $65.30   $65.30  
  Purchase #7 $231.33   9.247%   $252.7211   $252.72   $252.70   $252.70  
  7 purchase totals = $1,133.31       $1,245.1547   $1,245.15   $1,245.15   $1,245.20