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	$49.37	7.168%	$52.9088	$52.91	$52.90	$52.90
Purchase #2	$74.64	11.623%	$83.3154	$83.32	$83.30	$83.30
Purchase #3	$91.26	3.322%	$94.2917	$94.29	$94.30	$94.30
Purchase #4	$143.95	12.844%	$162.4389	$162.44	$162.45	$162.40
Purchase #5	$132.93	8.654%	$144.4338	$144.43	$144.45	$144.40
Purchase #6	$78.86	8.286%	$85.3943	$85.39	$85.40	$85.40
Purchase #7	$121.31	9.818%	$133.2202	$133.22	$133.20	$133.20
7 purchase totals =	$692.32		$756.0031	$756.00	$756.00	$755.90