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 $232.66   10.580%   $257.2754   $257.28   $257.30   $257.30  
  Purchase #2 $213.41   3.374%   $220.6105   $220.61   $220.60   $220.60  
  Purchase #3 $28.60   5.642%   $30.2136   $30.21   $30.20   $30.20  
  Purchase #4 $54.53   7.779%   $58.7719   $58.77   $58.75   $58.80  
  Purchase #5 $175.61   11.531%   $195.8596   $195.86   $195.85   $195.90  
  Purchase #6 $90.83   6.411%   $96.6531   $96.65   $96.65   $96.70  
  Purchase #7 $124.94   7.117%   $133.832   $133.83   $133.85   $133.80  
  7 purchase totals = $920.58       $993.2161   $993.21   $993.20   $993.30