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 $189.29   9.864%   $207.9616   $207.96   $207.95   $208.00  
  Purchase #2 $33.86   13.173%   $38.3204   $38.32   $38.30   $38.30  
  Purchase #3 $249.99   4.719%   $261.787   $261.79   $261.80   $261.80  
  Purchase #4 $197.92   4.253%   $206.3375   $206.34   $206.35   $206.30  
  Purchase #5 $134.59   10.195%   $148.3115   $148.31   $148.30   $148.30  
  Purchase #6 $29.84   4.765%   $31.2619   $31.26   $31.25   $31.30  
  Purchase #7 $152.64   6.395%   $162.4013   $162.40   $162.40   $162.40  
  7 purchase totals = $988.13       $1,056.3812   $1,056.38   $1,056.35   $1,056.40