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	$110.39	11.486%	$123.0694	$123.07	$123.05	$123.10
Purchase #2	$34.87	6.414%	$37.1066	$37.11	$37.10	$37.10
Purchase #3	$131.51	12.759%	$148.2894	$148.29	$148.30	$148.30
Purchase #4	$118.64	7.370%	$127.3838	$127.38	$127.40	$127.40
Purchase #5	$196.39	3.705%	$203.6662	$203.67	$203.65	$203.70
Purchase #6	$175.60	8.103%	$189.8289	$189.83	$189.85	$189.80
Purchase #7	$67.94	7.104%	$72.7665	$72.77	$72.75	$72.80
7 purchase totals =	$835.34		$902.1108	$902.12	$902.10	$902.20