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	$89.27	9.166%	$97.4525	$97.45	$97.45	$97.50
Purchase #2	$93.69	13.705%	$106.5302	$106.53	$106.55	$106.50
Purchase #3	$201.58	10.588%	$222.9233	$222.92	$222.90	$222.90
Purchase #4	$68.46	8.859%	$74.5249	$74.52	$74.50	$74.50
Purchase #5	$20.48	13.685%	$23.2827	$23.28	$23.30	$23.30
Purchase #6	$42.25	3.154%	$43.5826	$43.58	$43.60	$43.60
Purchase #7	$139.88	7.833%	$150.8368	$150.84	$150.85	$150.80
7 purchase totals =	$655.61		$719.1330	$719.12	$719.15	$719.10