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	$220.75	13.471%	$250.4872	$250.49	$250.50	$250.50
Purchase #2	$55.26	3.265%	$57.0642	$57.06	$57.05	$57.10
Purchase #3	$94.59	5.265%	$99.5702	$99.57	$99.55	$99.60
Purchase #4	$49.27	9.121%	$53.7639	$53.76	$53.75	$53.80
Purchase #5	$79.99	3.140%	$82.5017	$82.50	$82.50	$82.50
Purchase #6	$54.67	4.615%	$57.193	$57.19	$57.20	$57.20
Purchase #7	$160.93	4.823%	$168.6917	$168.69	$168.70	$168.70
7 purchase totals =	$715.46		$769.2719	$769.26	$769.25	$769.40