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	$72.87	10.537%	$80.5483	$80.55	$80.55	$80.50
Purchase #2	$233.52	3.836%	$242.4778	$242.48	$242.50	$242.50
Purchase #3	$10.37	4.658%	$10.853	$10.85	$10.85	$10.90
Purchase #4	$209.31	12.601%	$235.6852	$235.69	$235.70	$235.70
Purchase #5	$191.44	11.702%	$213.8423	$213.84	$213.85	$213.80
Purchase #6	$40.69	7.517%	$43.7487	$43.75	$43.75	$43.70
Purchase #7	$47.62	5.784%	$50.3743	$50.37	$50.35	$50.40
7 purchase totals =	$805.82		$877.5296	$877.53	$877.55	$877.50