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 $68.26   3.327%   $70.531   $70.53   $70.55   $70.50  
  Purchase #2 $130.70   4.595%   $136.7057   $136.71   $136.70   $136.70  
  Purchase #3 $76.74   7.168%   $82.2407   $82.24   $82.25   $82.20  
  Purchase #4 $116.52   7.137%   $124.836   $124.84   $124.85   $124.80  
  Purchase #5 $221.28   9.125%   $241.4718   $241.47   $241.45   $241.50  
  Purchase #6 $58.26   5.209%   $61.2948   $61.29   $61.30   $61.30  
  Purchase #7 $61.93   5.796%   $65.5195   $65.52   $65.50   $65.50  
  7 purchase totals = $733.69       $782.5995   $782.60   $782.60   $782.50