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 $56.96   7.700%   $61.3459   $61.35   $61.35   $61.30  
  Purchase #2 $93.73   8.186%   $101.4027   $101.40   $101.40   $101.40  
  Purchase #3 $63.47   7.551%   $68.2626   $68.26   $68.25   $68.30  
  Purchase #4 $126.38   12.112%   $141.6871   $141.69   $141.70   $141.70  
  Purchase #5 $222.56   8.610%   $241.7224   $241.72   $241.70   $241.70  
  Purchase #6 $68.50   5.210%   $72.0689   $72.07   $72.05   $72.10  
  Purchase #7 $154.36   12.573%   $173.7677   $173.77   $173.75   $173.80  
  7 purchase totals = $785.96       $860.2573   $860.26   $860.20   $860.30