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	$74.38	5.317%	$78.3348	$78.33	$78.35	$78.30
Purchase #2	$173.26	3.704%	$179.6776	$179.68	$179.70	$179.70
Purchase #3	$62.81	6.283%	$66.7564	$66.76	$66.75	$66.80
Purchase #4	$63.92	7.655%	$68.8131	$68.81	$68.80	$68.80
Purchase #5	$81.37	10.401%	$89.8333	$89.83	$89.85	$89.80
Purchase #6	$164.77	8.733%	$179.1594	$179.16	$179.15	$179.20
Purchase #7	$200.84	7.751%	$216.4071	$216.41	$216.40	$216.40
7 purchase totals =	$821.35		$878.9817	$878.98	$879.00	$879.00