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	$61.33	10.336%	$67.6691	$67.67	$67.65	$67.70
Purchase #2	$244.76	6.232%	$260.0134	$260.01	$260.00	$260.00
Purchase #3	$41.84	13.765%	$47.5993	$47.60	$47.60	$47.60
Purchase #4	$126.65	9.720%	$138.9604	$138.96	$138.95	$139.00
Purchase #5	$89.53	13.743%	$101.8341	$101.83	$101.85	$101.80
Purchase #6	$52.94	12.500%	$59.5575	$59.56	$59.55	$59.60
Purchase #7	$149.57	6.178%	$158.8104	$158.81	$158.80	$158.80
7 purchase totals =	$766.62		$834.4442	$834.44	$834.40	$834.50