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 $93.82   6.371%   $99.7973   $99.80   $99.80   $99.80  
  Purchase #2 $235.34   11.595%   $262.6277   $262.63   $262.65   $262.60  
  Purchase #3 $192.88   11.666%   $215.3814   $215.38   $215.40   $215.40  
  Purchase #4 $235.96   5.814%   $249.6787   $249.68   $249.70   $249.70  
  Purchase #5 $223.73   4.699%   $234.2431   $234.24   $234.25   $234.20  
  Purchase #6 $209.51   3.581%   $217.0126   $217.01   $217.00   $217.00  
  Purchase #7 $57.26   13.294%   $64.8721   $64.87   $64.85   $64.90  
  7 purchase totals = $1,248.50       $1,343.6129   $1,343.61   $1,343.65   $1,343.60