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	$19.51	7.237%	$20.9219	$20.92	$20.90	$20.90
Purchase #2	$190.51	6.838%	$203.5371	$203.54	$203.55	$203.50
Purchase #3	$182.42	7.352%	$195.8315	$195.83	$195.85	$195.80
Purchase #4	$82.69	8.622%	$89.8195	$89.82	$89.80	$89.80
Purchase #5	$109.98	12.193%	$123.3899	$123.39	$123.40	$123.40
Purchase #6	$115.33	10.579%	$127.5308	$127.53	$127.55	$127.50
Purchase #7	$39.50	6.391%	$42.0244	$42.02	$42.00	$42.00
7 purchase totals =	$739.94		$803.0551	$803.05	$803.05	$802.90