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	$147.70	4.862%	$154.8812	$154.88	$154.90	$154.90
Purchase #2	$25.67	3.309%	$26.5194	$26.52	$26.50	$26.50
Purchase #3	$152.50	12.701%	$171.869	$171.87	$171.85	$171.90
Purchase #4	$162.36	5.120%	$170.6728	$170.67	$170.65	$170.70
Purchase #5	$100.26	11.478%	$111.7678	$111.77	$111.75	$111.80
Purchase #6	$151.73	4.577%	$158.6747	$158.67	$158.65	$158.70
Purchase #7	$40.30	5.675%	$42.587	$42.59	$42.60	$42.60
7 purchase totals =	$780.52		$836.9719	$836.97	$836.90	$837.10