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	$181.74	9.436%	$198.889	$198.89	$198.90	$198.90
Purchase #2	$162.49	5.122%	$170.8127	$170.81	$170.80	$170.80
Purchase #3	$202.93	10.320%	$223.8724	$223.87	$223.85	$223.90
Purchase #4	$127.69	3.327%	$131.9382	$131.94	$131.95	$131.90
Purchase #5	$154.44	8.505%	$167.5751	$167.58	$167.60	$167.60
Purchase #6	$144.90	8.222%	$156.8137	$156.81	$156.80	$156.80
Purchase #7	$31.81	13.764%	$36.1883	$36.19	$36.20	$36.20
7 purchase totals =	$1,006.00		$1,086.0894	$1,086.09	$1,086.10	$1,086.10