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	$51.43	6.472%	$54.7585	$54.76	$54.75	$54.80
Purchase #2	$17.71	10.807%	$19.6239	$19.62	$19.60	$19.60
Purchase #3	$182.29	7.574%	$196.0966	$196.10	$196.10	$196.10
Purchase #4	$130.53	4.206%	$136.0201	$136.02	$136.00	$136.00
Purchase #5	$178.26	12.453%	$200.4587	$200.46	$200.45	$200.50
Purchase #6	$57.39	3.349%	$59.312	$59.31	$59.30	$59.30
Purchase #7	$170.55	4.369%	$178.0013	$178.00	$178.00	$178.00
7 purchase totals =	$788.16		$844.2711	$844.27	$844.20	$844.30