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	$72.65	10.634%	$80.3756	$80.38	$80.40	$80.40
Purchase #2	$68.98	13.494%	$78.2882	$78.29	$78.30	$78.30
Purchase #3	$244.92	8.739%	$266.3236	$266.32	$266.30	$266.30
Purchase #4	$160.69	11.426%	$179.0504	$179.05	$179.05	$179.10
Purchase #5	$6.75	6.393%	$7.1815	$7.18	$7.20	$7.20
Purchase #6	$196.65	6.765%	$209.9534	$209.95	$209.95	$210.00
Purchase #7	$214.82	3.292%	$221.8919	$221.89	$221.90	$221.90
7 purchase totals =	$965.46		$1,043.0646	$1,043.06	$1,043.10	$1,043.20