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 $93.36   3.399%   $96.5333   $96.53   $96.55   $96.50  
  Purchase #2 $67.54   12.189%   $75.7725   $75.77   $75.75   $75.80  
  Purchase #3 $77.28   7.845%   $83.3426   $83.34   $83.35   $83.30  
  Purchase #4 $122.48   8.207%   $132.5319   $132.53   $132.55   $132.50  
  Purchase #5 $248.56   8.582%   $269.8914   $269.89   $269.90   $269.90  
  Purchase #6 $189.25   13.511%   $214.8196   $214.82   $214.80   $214.80  
  Purchase #7 $38.66   12.263%   $43.4009   $43.40   $43.40   $43.40  
  7 purchase totals = $837.13       $916.2922   $916.28   $916.30   $916.20