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	$58.57	10.581%	$64.7673	$64.77	$64.75	$64.80
Purchase #2	$156.49	5.528%	$165.1408	$165.14	$165.15	$165.10
Purchase #3	$223.43	11.439%	$248.9882	$248.99	$249.00	$249.00
Purchase #4	$45.64	7.139%	$48.8982	$48.90	$48.90	$48.90
Purchase #5	$175.59	7.562%	$188.8681	$188.87	$188.85	$188.90
Purchase #6	$108.55	10.275%	$119.7035	$119.70	$119.70	$119.70
Purchase #7	$52.62	13.796%	$59.8795	$59.88	$59.90	$59.90
7 purchase totals =	$820.89		$896.2456	$896.25	$896.25	$896.30