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	$178.89	6.290%	$190.1422	$190.14	$190.15	$190.10
Purchase #2	$157.54	8.801%	$171.4051	$171.41	$171.40	$171.40
Purchase #3	$18.63	13.852%	$21.2106	$21.21	$21.20	$21.20
Purchase #4	$49.49	10.523%	$54.6978	$54.70	$54.70	$54.70
Purchase #5	$17.52	3.741%	$18.1754	$18.18	$18.20	$18.20
Purchase #6	$61.50	10.270%	$67.8161	$67.82	$67.80	$67.80
Purchase #7	$109.60	9.166%	$119.6459	$119.65	$119.65	$119.60
7 purchase totals =	$593.17		$643.0931	$643.11	$643.10	$643.00