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	$21.44	7.489%	$23.0456	$23.05	$23.05	$23.00
Purchase #2	$222.80	4.804%	$233.5033	$233.50	$233.50	$233.50
Purchase #3	$105.73	6.777%	$112.8953	$112.90	$112.90	$112.90
Purchase #4	$140.98	10.145%	$155.2824	$155.28	$155.30	$155.30
Purchase #5	$144.87	9.690%	$158.9079	$158.91	$158.90	$158.90
Purchase #6	$187.47	12.460%	$210.8288	$210.83	$210.85	$210.80
Purchase #7	$246.82	12.822%	$278.4673	$278.47	$278.45	$278.50
7 purchase totals =	$1,070.11		$1,172.9306	$1,172.94	$1,172.95	$1,172.90