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	$166.51	6.128%	$176.7137	$176.71	$176.70	$176.70
Purchase #2	$29.50	9.217%	$32.219	$32.22	$32.20	$32.20
Purchase #3	$179.29	13.544%	$203.573	$203.57	$203.55	$203.60
Purchase #4	$117.27	5.586%	$123.8207	$123.82	$123.80	$123.80
Purchase #5	$72.30	11.127%	$80.3448	$80.34	$80.35	$80.30
Purchase #6	$223.33	12.160%	$250.4869	$250.49	$250.50	$250.50
Purchase #7	$95.42	10.846%	$105.7693	$105.77	$105.75	$105.80
7 purchase totals =	$883.62		$972.9274	$972.92	$972.85	$972.90