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 $224.72   10.785%   $248.9561   $248.96   $248.95   $249.00  
  Purchase #2 $228.77   7.369%   $245.6281   $245.63   $245.65   $245.60  
  Purchase #3 $180.66   8.867%   $196.6791   $196.68   $196.70   $196.70  
  Purchase #4 $5.73   8.420%   $6.2125   $6.21   $6.20   $6.20  
  Purchase #5 $197.80   4.355%   $206.4142   $206.41   $206.40   $206.40  
  Purchase #6 $50.94   12.561%   $57.3386   $57.34   $57.35   $57.30  
  Purchase #7 $168.88   12.503%   $189.9951   $190.00   $190.00   $190.00  
  7 purchase totals = $1,057.50       $1,151.2237   $1,151.23   $1,151.25   $1,151.20