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	$111.88	9.494%	$122.5019	$122.50	$122.50	$122.50
Purchase #2	$151.97	4.843%	$159.3299	$159.33	$159.35	$159.30
Purchase #3	$82.66	8.731%	$89.877	$89.88	$89.90	$89.90
Purchase #4	$25.26	10.645%	$27.9489	$27.95	$27.95	$27.90
Purchase #5	$109.40	3.379%	$113.0966	$113.10	$113.10	$113.10
Purchase #6	$101.59	3.234%	$104.8754	$104.88	$104.90	$104.90
Purchase #7	$58.71	3.517%	$60.7748	$60.77	$60.75	$60.80
7 purchase totals =	$641.47		$678.4045	$678.41	$678.45	$678.40