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 $56.45   7.564%   $60.7199   $60.72   $60.70   $60.70  
  Purchase #2 $61.69   10.761%   $68.3285   $68.33   $68.35   $68.30  
  Purchase #3 $130.46   3.688%   $135.2714   $135.27   $135.25   $135.30  
  Purchase #4 $148.37   9.456%   $162.3999   $162.40   $162.40   $162.40  
  Purchase #5 $44.90   12.349%   $50.4447   $50.44   $50.45   $50.40  
  Purchase #6 $250.33   4.559%   $261.7425   $261.74   $261.75   $261.70  
  Purchase #7 $113.98   4.644%   $119.2732   $119.27   $119.25   $119.30  
  7 purchase totals = $806.18       $858.1801   $858.17   $858.15   $858.10