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 $56.76   9.126%   $61.9399   $61.94   $61.95   $61.90  
  Purchase #2 $222.43   7.739%   $239.6439   $239.64   $239.65   $239.60  
  Purchase #3 $151.88   9.188%   $165.8347   $165.83   $165.85   $165.80  
  Purchase #4 $50.77   10.559%   $56.1308   $56.13   $56.15   $56.10  
  Purchase #5 $248.90   10.515%   $275.0718   $275.07   $275.05   $275.10  
  Purchase #6 $225.79   9.126%   $246.3956   $246.40   $246.40   $246.40  
  Purchase #7 $169.97   13.540%   $192.9839   $192.98   $193.00   $193.00  
  7 purchase totals = $1,126.50       $1,238.0006   $1,237.99   $1,238.05   $1,237.90