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 $21.27   12.782%   $23.9887   $23.99   $24.00   $24.00  
  Purchase #2 $152.56   9.636%   $167.2607   $167.26   $167.25   $167.30  
  Purchase #3 $146.98   10.264%   $162.066   $162.07   $162.05   $162.10  
  Purchase #4 $202.55   5.104%   $212.8882   $212.89   $212.90   $212.90  
  Purchase #5 $62.57   4.174%   $65.1817   $65.18   $65.20   $65.20  
  Purchase #6 $6.91   9.207%   $7.5462   $7.55   $7.55   $7.50  
  Purchase #7 $218.38   3.613%   $226.2701   $226.27   $226.25   $226.30  
  7 purchase totals = $811.22       $865.2016   $865.21   $865.20   $865.30