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 $173.90   13.377%   $197.1626   $197.16   $197.15   $197.20  
  Purchase #2 $101.61   12.801%   $114.6171   $114.62   $114.60   $114.60  
  Purchase #3 $31.28   8.134%   $33.8243   $33.82   $33.80   $33.80  
  Purchase #4 $249.77   6.501%   $266.0075   $266.01   $266.00   $266.00  
  Purchase #5 $223.34   9.713%   $245.033   $245.03   $245.05   $245.00  
  Purchase #6 $206.71   5.460%   $217.9964   $218.00   $218.00   $218.00  
  Purchase #7 $171.75   3.270%   $177.3662   $177.37   $177.35   $177.40  
  7 purchase totals = $1,158.36       $1,252.0071   $1,252.01   $1,251.95   $1,252.00