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	$85.45	12.809%	$96.3953	$96.40	$96.40	$96.40
Purchase #2	$224.37	9.250%	$245.1242	$245.12	$245.10	$245.10
Purchase #3	$32.54	11.627%	$36.3234	$36.32	$36.30	$36.30
Purchase #4	$243.88	10.641%	$269.8313	$269.83	$269.85	$269.80
Purchase #5	$90.67	10.814%	$100.4751	$100.48	$100.50	$100.50
Purchase #6	$170.54	13.212%	$193.0717	$193.07	$193.05	$193.10
Purchase #7	$92.32	6.604%	$98.4168	$98.42	$98.40	$98.40
7 purchase totals =	$939.77		$1,039.6378	$1,039.64	$1,039.60	$1,039.60