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 $95.41   13.201%   $108.0051   $108.01   $108.00   $108.00  
  Purchase #2 $112.96   6.779%   $120.6176   $120.62   $120.60   $120.60  
  Purchase #3 $83.92   8.157%   $90.7654   $90.77   $90.75   $90.80  
  Purchase #4 $151.64   10.270%   $167.2134   $167.21   $167.20   $167.20  
  Purchase #5 $109.91   3.278%   $113.5128   $113.51   $113.50   $113.50  
  Purchase #6 $160.61   9.746%   $176.2631   $176.26   $176.25   $176.30  
  Purchase #7 $248.42   5.300%   $261.5863   $261.59   $261.60   $261.60  
  7 purchase totals = $962.87       $1,037.9637   $1,037.97   $1,037.90   $1,038.00