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 $183.78   12.194%   $206.1901   $206.19   $206.20   $206.20  
  Purchase #2 $60.33   13.266%   $68.3334   $68.33   $68.35   $68.30  
  Purchase #3 $11.39   3.175%   $11.7516   $11.75   $11.75   $11.80  
  Purchase #4 $225.78   9.342%   $246.8724   $246.87   $246.85   $246.90  
  Purchase #5 $218.25   13.720%   $248.1939   $248.19   $248.20   $248.20  
  Purchase #6 $166.37   12.597%   $187.3276   $187.33   $187.35   $187.30  
  Purchase #7 $245.40   11.514%   $273.6554   $273.66   $273.65   $273.70  
  7 purchase totals = $1,111.30       $1,242.3244   $1,242.32   $1,242.35   $1,242.40