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 $59.65   12.466%   $67.086   $67.09   $67.10   $67.10  
  Purchase #2 $29.55   4.769%   $30.9592   $30.96   $30.95   $31.00  
  Purchase #3 $47.29   11.599%   $52.7752   $52.78   $52.80   $52.80  
  Purchase #4 $249.49   4.620%   $261.0164   $261.02   $261.00   $261.00  
  Purchase #5 $194.96   13.197%   $220.6889   $220.69   $220.70   $220.70  
  Purchase #6 $202.73   11.346%   $225.7317   $225.73   $225.75   $225.70  
  Purchase #7 $69.71   9.738%   $76.4984   $76.50   $76.50   $76.50  
  7 purchase totals = $853.38       $934.7558   $934.77   $934.80   $934.80