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 $56.68   8.835%   $61.6877   $61.69   $61.70   $61.70  
  Purchase #2 $169.96   8.830%   $184.9675   $184.97   $184.95   $185.00  
  Purchase #3 $196.40   9.231%   $214.5297   $214.53   $214.55   $214.50  
  Purchase #4 $66.48   10.859%   $73.6991   $73.70   $73.70   $73.70  
  Purchase #5 $104.38   10.335%   $115.1677   $115.17   $115.15   $115.20  
  Purchase #6 $192.30   4.225%   $200.4247   $200.42   $200.40   $200.40  
  Purchase #7 $165.98   12.742%   $187.1292   $187.13   $187.15   $187.10  
  7 purchase totals = $952.18       $1,037.6056   $1,037.61   $1,037.60   $1,037.60