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 $67.30   5.807%   $71.2081   $71.21   $71.20   $71.20  
  Purchase #2 $210.59   12.549%   $237.0169   $237.02   $237.00   $237.00  
  Purchase #3 $154.94   6.493%   $165.0003   $165.00   $165.00   $165.00  
  Purchase #4 $96.57   4.632%   $101.0431   $101.04   $101.05   $101.00  
  Purchase #5 $224.87   6.558%   $239.617   $239.62   $239.60   $239.60  
  Purchase #6 $235.54   9.208%   $257.2285   $257.23   $257.25   $257.20  
  Purchase #7 $9.52   4.707%   $9.9681   $9.97   $9.95   $10.00  
  7 purchase totals = $999.33       $1,081.0820   $1,081.09   $1,081.05   $1,081.00