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 $88.46   11.181%   $98.3507   $98.35   $98.35   $98.40  
  Purchase #2 $8.75   9.399%   $9.5724   $9.57   $9.55   $9.60  
  Purchase #3 $48.96   6.448%   $52.1169   $52.12   $52.10   $52.10  
  Purchase #4 $162.74   5.326%   $171.4075   $171.41   $171.40   $171.40  
  Purchase #5 $218.39   3.770%   $226.6233   $226.62   $226.60   $226.60  
  Purchase #6 $232.41   12.723%   $261.9795   $261.98   $262.00   $262.00  
  Purchase #7 $234.75   5.349%   $247.3068   $247.31   $247.30   $247.30  
  7 purchase totals = $994.46       $1,067.3571   $1,067.36   $1,067.30   $1,067.40