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	$91.89	8.202%	$99.4268	$99.43	$99.45	$99.40
Purchase #2	$15.70	9.420%	$17.1789	$17.18	$17.20	$17.20
Purchase #3	$178.86	3.216%	$184.6121	$184.61	$184.60	$184.60
Purchase #4	$117.90	12.711%	$132.8863	$132.89	$132.90	$132.90
Purchase #5	$165.54	13.848%	$188.464	$188.46	$188.45	$188.50
Purchase #6	$175.54	5.354%	$184.9384	$184.94	$184.95	$184.90
Purchase #7	$39.73	4.760%	$41.6211	$41.62	$41.60	$41.60
7 purchase totals =	$785.16		$849.1276	$849.13	$849.15	$849.10