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	$200.60	9.444%	$219.5447	$219.54	$219.55	$219.50
Purchase #2	$49.91	4.868%	$52.3396	$52.34	$52.35	$52.30
Purchase #3	$180.25	9.103%	$196.6582	$196.66	$196.65	$196.70
Purchase #4	$154.73	7.251%	$165.9495	$165.95	$165.95	$165.90
Purchase #5	$105.88	6.634%	$112.9041	$112.90	$112.90	$112.90
Purchase #6	$74.67	9.857%	$82.0302	$82.03	$82.05	$82.00
Purchase #7	$132.91	13.139%	$150.373	$150.37	$150.35	$150.40
7 purchase totals =	$898.95		$979.7993	$979.79	$979.80	$979.70