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 $125.61   9.655%   $137.7376   $137.74   $137.75   $137.70  
  Purchase #2 $98.62   8.870%   $107.3676   $107.37   $107.35   $107.40  
  Purchase #3 $246.35   9.485%   $269.7163   $269.72   $269.70   $269.70  
  Purchase #4 $63.38   11.245%   $70.5071   $70.51   $70.50   $70.50  
  Purchase #5 $119.61   12.394%   $134.4345   $134.43   $134.45   $134.40  
  Purchase #6 $116.44   5.429%   $122.7615   $122.76   $122.75   $122.80  
  Purchase #7 $168.53   4.841%   $176.6885   $176.69   $176.70   $176.70  
  7 purchase totals = $938.54       $1,019.2131   $1,019.22   $1,019.20   $1,019.20