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	$51.80	7.851%	$55.8668	$55.87	$55.85	$55.90
Purchase #2	$123.91	3.254%	$127.942	$127.94	$127.95	$127.90
Purchase #3	$85.71	4.348%	$89.4367	$89.44	$89.45	$89.40
Purchase #4	$223.97	10.263%	$246.956	$246.96	$246.95	$247.00
Purchase #5	$153.93	4.555%	$160.9415	$160.94	$160.95	$160.90
Purchase #6	$87.37	8.209%	$94.5422	$94.54	$94.55	$94.50
Purchase #7	$173.70	3.235%	$179.3192	$179.32	$179.30	$179.30
7 purchase totals =	$900.39		$955.0044	$955.01	$955.00	$954.90