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	$29.86	8.204%	$32.3097	$32.31	$32.30	$32.30
Purchase #2	$97.30	6.832%	$103.9475	$103.95	$103.95	$103.90
Purchase #3	$241.76	11.153%	$268.7235	$268.72	$268.70	$268.70
Purchase #4	$107.61	6.551%	$114.6595	$114.66	$114.65	$114.70
Purchase #5	$48.95	5.379%	$51.583	$51.58	$51.60	$51.60
Purchase #6	$89.46	5.702%	$94.561	$94.56	$94.55	$94.60
Purchase #7	$220.89	13.329%	$250.3324	$250.33	$250.35	$250.30
7 purchase totals =	$835.83		$916.1166	$916.11	$916.10	$916.10