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	$87.68	13.151%	$99.2108	$99.21	$99.20	$99.20
Purchase #2	$66.42	12.327%	$74.6076	$74.61	$74.60	$74.60
Purchase #3	$148.87	13.728%	$169.3069	$169.31	$169.30	$169.30
Purchase #4	$226.73	12.272%	$254.5543	$254.55	$254.55	$254.60
Purchase #5	$169.32	10.172%	$186.5432	$186.54	$186.55	$186.50
Purchase #6	$31.89	4.633%	$33.3675	$33.37	$33.35	$33.40
Purchase #7	$55.98	5.434%	$59.022	$59.02	$59.00	$59.00
7 purchase totals =	$786.89		$876.6123	$876.61	$876.55	$876.60