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 $51.74   9.426%   $56.617   $56.62   $56.60   $56.60  
  Purchase #2 $136.29   4.851%   $142.9014   $142.90   $142.90   $142.90  
  Purchase #3 $23.32   10.170%   $25.6916   $25.69   $25.70   $25.70  
  Purchase #4 $61.97   5.672%   $65.4849   $65.48   $65.50   $65.50  
  Purchase #5 $165.38   4.661%   $173.0884   $173.09   $173.10   $173.10  
  Purchase #6 $152.86   3.586%   $158.3416   $158.34   $158.35   $158.30  
  Purchase #7 $224.66   11.869%   $251.3249   $251.32   $251.30   $251.30  
  7 purchase totals = $816.22       $873.4498   $873.44   $873.45   $873.40