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	$210.86	9.198%	$230.2549	$230.25	$230.25	$230.30
Purchase #2	$158.52	8.746%	$172.3842	$172.38	$172.40	$172.40
Purchase #3	$186.59	11.694%	$208.4098	$208.41	$208.40	$208.40
Purchase #4	$212.85	7.156%	$228.0815	$228.08	$228.10	$228.10
Purchase #5	$81.83	9.329%	$89.4639	$89.46	$89.45	$89.50
Purchase #6	$46.33	3.141%	$47.7852	$47.79	$47.80	$47.80
Purchase #7	$104.89	10.516%	$115.9202	$115.92	$115.90	$115.90
7 purchase totals =	$1,001.87		$1,092.2997	$1,092.29	$1,092.30	$1,092.40