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 $62.91   13.264%   $71.2544   $71.25   $71.25   $71.30  
  Purchase #2 $58.88   10.574%   $65.106   $65.11   $65.10   $65.10  
  Purchase #3 $221.81   3.164%   $228.8281   $228.83   $228.85   $228.80  
  Purchase #4 $229.78   13.815%   $261.5241   $261.52   $261.50   $261.50  
  Purchase #5 $232.90   12.576%   $262.1895   $262.19   $262.20   $262.20  
  Purchase #6 $248.61   8.497%   $269.7344   $269.73   $269.75   $269.70  
  Purchase #7 $116.37   6.837%   $124.3262   $124.33   $124.35   $124.30  
  7 purchase totals = $1,171.26       $1,282.9627   $1,282.96   $1,283.00   $1,282.90