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	$47.96	10.853%	$53.1651	$53.17	$53.15	$53.20
Purchase #2	$171.71	7.312%	$184.2654	$184.27	$184.25	$184.30
Purchase #3	$56.39	5.676%	$59.5907	$59.59	$59.60	$59.60
Purchase #4	$10.77	12.788%	$12.1473	$12.15	$12.15	$12.10
Purchase #5	$112.97	13.196%	$127.8775	$127.88	$127.90	$127.90
Purchase #6	$194.67	8.779%	$211.7601	$211.76	$211.75	$211.80
Purchase #7	$45.89	6.633%	$48.9339	$48.93	$48.95	$48.90
7 purchase totals =	$640.36		$697.7400	$697.75	$697.75	$697.80