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	$93.83	4.777%	$98.3123	$98.31	$98.30	$98.30
Purchase #2	$43.69	7.273%	$46.8676	$46.87	$46.85	$46.90
Purchase #3	$119.27	6.680%	$127.2372	$127.24	$127.25	$127.20
Purchase #4	$79.26	12.395%	$89.0843	$89.08	$89.10	$89.10
Purchase #5	$13.44	8.687%	$14.6075	$14.61	$14.60	$14.60
Purchase #6	$222.52	4.743%	$233.0741	$233.07	$233.05	$233.10
Purchase #7	$50.55	13.642%	$57.446	$57.45	$57.45	$57.40
7 purchase totals =	$622.56		$666.6290	$666.63	$666.60	$666.60