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 $218.63   10.417%   $241.4047   $241.40   $241.40   $241.40  
  Purchase #2 $194.32   6.326%   $206.6127   $206.61   $206.60   $206.60  
  Purchase #3 $176.36   6.472%   $187.774   $187.77   $187.75   $187.80  
  Purchase #4 $230.65   7.734%   $248.4885   $248.49   $248.50   $248.50  
  Purchase #5 $241.59   11.656%   $269.7497   $269.75   $269.75   $269.70  
  Purchase #6 $87.81   12.674%   $98.939   $98.94   $98.95   $98.90  
  Purchase #7 $179.96   13.235%   $203.7777   $203.78   $203.80   $203.80  
  7 purchase totals = $1,329.32       $1,456.7463   $1,456.74   $1,456.75   $1,456.70