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	$171.53	4.633%	$179.477	$179.48	$179.50	$179.50
Purchase #2	$151.82	4.107%	$158.0552	$158.06	$158.05	$158.10
Purchase #3	$74.42	7.869%	$80.2761	$80.28	$80.30	$80.30
Purchase #4	$43.55	3.457%	$45.0555	$45.06	$45.05	$45.10
Purchase #5	$106.75	5.606%	$112.7344	$112.73	$112.75	$112.70
Purchase #6	$66.84	11.798%	$74.7258	$74.73	$74.75	$74.70
Purchase #7	$119.42	6.800%	$127.5406	$127.54	$127.55	$127.50
7 purchase totals =	$734.33		$777.8646	$777.88	$777.95	$777.90