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 $55.94   9.416%   $61.2073   $61.21   $61.20   $61.20  
  Purchase #2 $88.59   8.842%   $96.4231   $96.42   $96.40   $96.40  
  Purchase #3 $158.96   10.553%   $175.735   $175.74   $175.75   $175.70  
  Purchase #4 $89.83   13.113%   $101.6094   $101.61   $101.60   $101.60  
  Purchase #5 $76.47   10.843%   $84.7616   $84.76   $84.75   $84.80  
  Purchase #6 $145.66   3.161%   $150.2643   $150.26   $150.25   $150.30  
  Purchase #7 $92.43   10.237%   $101.8921   $101.89   $101.90   $101.90  
  7 purchase totals = $707.88       $771.8928   $771.89   $771.85   $771.90