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 $116.73   9.820%   $128.1929   $128.19   $128.20   $128.20  
  Purchase #2 $114.72   6.535%   $122.217   $122.22   $122.20   $122.20  
  Purchase #3 $141.25   12.835%   $159.3794   $159.38   $159.40   $159.40  
  Purchase #4 $50.47   11.187%   $56.1161   $56.12   $56.10   $56.10  
  Purchase #5 $142.74   10.154%   $157.2338   $157.23   $157.25   $157.20  
  Purchase #6 $62.48   11.568%   $69.7077   $69.71   $69.70   $69.70  
  Purchase #7 $5.47   11.393%   $6.0932   $6.09   $6.10   $6.10  
  7 purchase totals = $633.86       $698.9401   $698.94   $698.95   $698.90