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 $95.35   3.772%   $98.9466   $98.95   $98.95   $98.90  
  Purchase #2 $68.69   7.174%   $73.6178   $73.62   $73.60   $73.60  
  Purchase #3 $132.53   9.376%   $144.956   $144.96   $144.95   $145.00  
  Purchase #4 $111.48   4.599%   $116.607   $116.61   $116.60   $116.60  
  Purchase #5 $60.92   6.522%   $64.8932   $64.89   $64.90   $64.90  
  Purchase #6 $235.26   3.837%   $244.2869   $244.29   $244.30   $244.30  
  Purchase #7 $87.67   13.695%   $99.6764   $99.68   $99.70   $99.70  
  7 purchase totals = $791.90       $842.9839   $843.00   $843.00   $843.00