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	$243.64	11.206%	$270.9423	$270.94	$270.95	$270.90
Purchase #2	$132.49	11.128%	$147.2335	$147.23	$147.25	$147.20
Purchase #3	$195.28	13.823%	$222.2736	$222.27	$222.25	$222.30
Purchase #4	$114.55	10.211%	$126.2467	$126.25	$126.25	$126.20
Purchase #5	$137.39	5.352%	$144.7431	$144.74	$144.75	$144.70
Purchase #6	$78.94	12.873%	$89.1019	$89.10	$89.10	$89.10
Purchase #7	$163.69	13.407%	$185.6359	$185.64	$185.65	$185.60
7 purchase totals =	$1,065.98		$1,186.1770	$1,186.17	$1,186.20	$1,186.00