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	$236.40	6.699%	$252.2364	$252.24	$252.25	$252.20
Purchase #2	$211.47	5.370%	$222.8259	$222.83	$222.85	$222.80
Purchase #3	$18.65	12.254%	$20.9354	$20.94	$20.95	$20.90
Purchase #4	$127.96	7.410%	$137.4418	$137.44	$137.45	$137.40
Purchase #5	$143.38	6.215%	$152.2911	$152.29	$152.30	$152.30
Purchase #6	$241.42	12.183%	$270.8322	$270.83	$270.85	$270.80
Purchase #7	$105.63	7.501%	$113.5533	$113.55	$113.55	$113.60
7 purchase totals =	$1,084.91		$1,170.1161	$1,170.12	$1,170.20	$1,170.00