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 $64.27   3.751%   $66.6808   $66.68   $66.70   $66.70  
  Purchase #2 $161.71   13.115%   $182.9183   $182.92   $182.90   $182.90  
  Purchase #3 $166.68   3.605%   $172.6888   $172.69   $172.70   $172.70  
  Purchase #4 $55.90   8.548%   $60.6783   $60.68   $60.70   $60.70  
  Purchase #5 $177.51   9.574%   $194.5048   $194.50   $194.50   $194.50  
  Purchase #6 $64.33   9.556%   $70.4774   $70.48   $70.50   $70.50  
  Purchase #7 $35.41   7.328%   $38.0048   $38.00   $38.00   $38.00  
  7 purchase totals = $725.81       $785.9532   $785.95   $786.00   $786.00