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 $44.36   8.227%   $48.0095   $48.01   $48.00   $48.00  
  Purchase #2 $22.80   4.336%   $23.7886   $23.79   $23.80   $23.80  
  Purchase #3 $165.58   6.720%   $176.707   $176.71   $176.70   $176.70  
  Purchase #4 $30.76   12.312%   $34.5472   $34.55   $34.55   $34.50  
  Purchase #5 $244.26   12.449%   $274.6679   $274.67   $274.65   $274.70  
  Purchase #6 $178.84   8.473%   $193.9931   $193.99   $194.00   $194.00  
  Purchase #7 $30.61   12.231%   $34.3539   $34.35   $34.35   $34.40  
  7 purchase totals = $717.21       $786.0672   $786.07   $786.05   $786.10