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	$32.46	8.728%	$35.2931	$35.29	$35.30	$35.30
Purchase #2	$97.30	8.474%	$105.5452	$105.55	$105.55	$105.50
Purchase #3	$142.49	11.586%	$158.9989	$159.00	$159.00	$159.00
Purchase #4	$190.27	11.658%	$212.4517	$212.45	$212.45	$212.50
Purchase #5	$122.92	13.862%	$139.9592	$139.96	$139.95	$140.00
Purchase #6	$142.48	4.161%	$148.4086	$148.41	$148.40	$148.40
Purchase #7	$86.51	11.832%	$96.7459	$96.75	$96.75	$96.70
7 purchase totals =	$814.43		$897.4026	$897.41	$897.40	$897.40