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 $60.46   9.735%   $66.3458   $66.35   $66.35   $66.30  
  Purchase #2 $229.29   3.426%   $237.1455   $237.15   $237.15   $237.10  
  Purchase #3 $176.45   6.661%   $188.2033   $188.20   $188.20   $188.20  
  Purchase #4 $88.66   7.795%   $95.571   $95.57   $95.55   $95.60  
  Purchase #5 $82.51   13.772%   $93.8733   $93.87   $93.85   $93.90  
  Purchase #6 $65.56   9.104%   $71.5286   $71.53   $71.55   $71.50  
  Purchase #7 $237.66   6.487%   $253.077   $253.08   $253.10   $253.10  
  7 purchase totals = $940.59       $1,005.7445   $1,005.75   $1,005.75   $1,005.70