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	$100.30	9.530%	$109.8586	$109.86	$109.85	$109.90
Purchase #2	$27.40	13.603%	$31.1272	$31.13	$31.15	$31.10
Purchase #3	$127.89	13.873%	$145.6322	$145.63	$145.65	$145.60
Purchase #4	$235.99	11.336%	$262.7418	$262.74	$262.75	$262.70
Purchase #5	$124.35	7.143%	$133.2323	$133.23	$133.25	$133.20
Purchase #6	$129.63	10.284%	$142.9611	$142.96	$142.95	$143.00
Purchase #7	$76.26	13.170%	$86.3034	$86.30	$86.30	$86.30
7 purchase totals =	$821.82		$911.8566	$911.85	$911.90	$911.80