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	$250.59	6.214%	$266.1617	$266.16	$266.15	$266.20
Purchase #2	$133.43	12.783%	$150.4864	$150.49	$150.50	$150.50
Purchase #3	$54.75	13.248%	$62.0033	$62.00	$62.00	$62.00
Purchase #4	$18.76	11.365%	$20.8921	$20.89	$20.90	$20.90
Purchase #5	$149.64	3.385%	$154.7053	$154.71	$154.70	$154.70
Purchase #6	$54.72	8.114%	$59.16	$59.16	$59.15	$59.20
Purchase #7	$67.88	5.304%	$71.4804	$71.48	$71.50	$71.50
7 purchase totals =	$729.77		$784.8892	$784.89	$784.90	$785.00