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 $208.96   12.541%   $235.1657   $235.17   $235.15   $235.20  
  Purchase #2 $53.84   13.144%   $60.9167   $60.92   $60.90   $60.90  
  Purchase #3 $156.26   12.169%   $175.2753   $175.28   $175.30   $175.30  
  Purchase #4 $221.92   11.380%   $247.1745   $247.17   $247.15   $247.20  
  Purchase #5 $167.52   9.543%   $183.5064   $183.51   $183.50   $183.50  
  Purchase #6 $76.42   10.656%   $84.5633   $84.56   $84.55   $84.60  
  Purchase #7 $73.41   10.638%   $81.2194   $81.22   $81.20   $81.20  
  7 purchase totals = $958.33       $1,067.8213   $1,067.83   $1,067.75   $1,067.90