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	$51.60	5.368%	$54.3699	$54.37	$54.35	$54.40
Purchase #2	$184.60	4.674%	$193.2282	$193.23	$193.25	$193.20
Purchase #3	$160.62	8.816%	$174.7803	$174.78	$174.80	$174.80
Purchase #4	$189.56	3.460%	$196.1188	$196.12	$196.10	$196.10
Purchase #5	$56.90	10.121%	$62.6588	$62.66	$62.65	$62.70
Purchase #6	$209.89	8.599%	$227.9384	$227.94	$227.95	$227.90
Purchase #7	$60.77	6.676%	$64.827	$64.83	$64.85	$64.80
7 purchase totals =	$913.94		$973.9214	$973.93	$973.95	$973.90