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	$62.61	13.781%	$71.2383	$71.24	$71.25	$71.20
Purchase #2	$130.64	9.764%	$143.3957	$143.40	$143.40	$143.40
Purchase #3	$118.85	10.784%	$131.6668	$131.67	$131.65	$131.70
Purchase #4	$191.64	13.697%	$217.8889	$217.89	$217.90	$217.90
Purchase #5	$85.56	6.153%	$90.8245	$90.82	$90.80	$90.80
Purchase #6	$84.62	4.809%	$88.6894	$88.69	$88.70	$88.70
Purchase #7	$226.56	3.597%	$234.7094	$234.71	$234.70	$234.70
7 purchase totals =	$900.48		$978.4130	$978.42	$978.40	$978.40