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	$52.42	6.618%	$55.8892	$55.89	$55.90	$55.90
Purchase #2	$30.82	6.872%	$32.938	$32.94	$32.95	$32.90
Purchase #3	$223.49	13.568%	$253.8131	$253.81	$253.80	$253.80
Purchase #4	$160.90	12.814%	$181.5177	$181.52	$181.50	$181.50
Purchase #5	$142.72	11.493%	$159.1228	$159.12	$159.10	$159.10
Purchase #6	$14.84	10.739%	$16.4337	$16.43	$16.45	$16.40
Purchase #7	$95.63	7.248%	$102.5613	$102.56	$102.55	$102.60
7 purchase totals =	$720.82		$802.2758	$802.27	$802.25	$802.20