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	$158.81	9.264%	$173.5222	$173.52	$173.50	$173.50
Purchase #2	$233.69	8.847%	$254.3646	$254.36	$254.35	$254.40
Purchase #3	$85.32	8.484%	$92.5585	$92.56	$92.55	$92.60
Purchase #4	$208.60	7.106%	$223.4231	$223.42	$223.40	$223.40
Purchase #5	$181.25	7.153%	$194.2148	$194.21	$194.20	$194.20
Purchase #6	$206.61	7.855%	$222.8392	$222.84	$222.85	$222.80
Purchase #7	$16.87	9.409%	$18.4573	$18.46	$18.45	$18.50
7 purchase totals =	$1,091.15		$1,179.3797	$1,179.37	$1,179.30	$1,179.40