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	$17.46	3.269%	$18.0308	$18.03	$18.05	$18.00
Purchase #2	$101.66	9.560%	$111.3787	$111.38	$111.40	$111.40
Purchase #3	$84.49	3.628%	$87.5553	$87.56	$87.55	$87.60
Purchase #4	$89.41	10.753%	$99.0243	$99.02	$99.00	$99.00
Purchase #5	$35.78	12.539%	$40.2665	$40.27	$40.25	$40.30
Purchase #6	$96.58	9.447%	$105.7039	$105.70	$105.70	$105.70
Purchase #7	$145.63	7.332%	$156.3076	$156.31	$156.30	$156.30
7 purchase totals =	$571.01		$618.2671	$618.27	$618.25	$618.30