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	$191.90	12.721%	$216.3116	$216.31	$216.30	$216.30
Purchase #2	$184.48	10.825%	$204.45	$204.45	$204.45	$204.50
Purchase #3	$233.91	12.543%	$263.2493	$263.25	$263.25	$263.20
Purchase #4	$91.73	8.216%	$99.2665	$99.27	$99.25	$99.30
Purchase #5	$99.35	10.102%	$109.3863	$109.39	$109.40	$109.40
Purchase #6	$35.56	8.462%	$38.5691	$38.57	$38.55	$38.60
Purchase #7	$233.92	8.327%	$253.3985	$253.40	$253.40	$253.40
7 purchase totals =	$1,070.85		$1,184.6313	$1,184.64	$1,184.60	$1,184.70