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	$99.57	13.637%	$113.1484	$113.15	$113.15	$113.10
Purchase #2	$162.69	3.724%	$168.7486	$168.75	$168.75	$168.70
Purchase #3	$171.55	13.186%	$194.1706	$194.17	$194.15	$194.20
Purchase #4	$238.65	8.467%	$258.8565	$258.86	$258.85	$258.90
Purchase #5	$65.72	11.705%	$73.4125	$73.41	$73.40	$73.40
Purchase #6	$16.89	7.271%	$18.1181	$18.12	$18.10	$18.10
Purchase #7	$234.60	12.716%	$264.4317	$264.43	$264.45	$264.40
7 purchase totals =	$989.67		$1,090.8864	$1,090.89	$1,090.85	$1,090.80