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	$106.79	4.742%	$111.854	$111.85	$111.85	$111.90
Purchase #2	$86.63	9.395%	$94.7689	$94.77	$94.75	$94.80
Purchase #3	$151.96	4.337%	$158.5505	$158.55	$158.55	$158.60
Purchase #4	$85.74	3.132%	$88.4254	$88.43	$88.45	$88.40
Purchase #5	$84.69	8.463%	$91.8573	$91.86	$91.85	$91.90
Purchase #6	$171.99	10.706%	$190.4032	$190.40	$190.40	$190.40
Purchase #7	$154.57	10.473%	$170.7581	$170.76	$170.75	$170.80
7 purchase totals =	$842.37		$906.6174	$906.62	$906.60	$906.80