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	$167.46	6.488%	$178.3248	$178.32	$178.30	$178.30
Purchase #2	$83.75	13.723%	$95.243	$95.24	$95.25	$95.20
Purchase #3	$123.63	12.874%	$139.5461	$139.55	$139.55	$139.50
Purchase #4	$53.82	13.625%	$61.153	$61.15	$61.15	$61.20
Purchase #5	$185.76	4.343%	$193.8276	$193.83	$193.85	$193.80
Purchase #6	$13.62	13.185%	$15.4158	$15.42	$15.40	$15.40
Purchase #7	$17.89	9.199%	$19.5357	$19.54	$19.55	$19.50
7 purchase totals =	$645.93		$703.0460	$703.05	$703.05	$702.90