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	$99.51	13.437%	$112.8812	$112.88	$112.90	$112.90
Purchase #2	$197.40	8.425%	$214.031	$214.03	$214.05	$214.00
Purchase #3	$146.91	13.623%	$166.9235	$166.92	$166.90	$166.90
Purchase #4	$215.68	9.319%	$235.7792	$235.78	$235.80	$235.80
Purchase #5	$158.76	10.869%	$176.0156	$176.02	$176.00	$176.00
Purchase #6	$111.64	4.653%	$116.8346	$116.83	$116.85	$116.80
Purchase #7	$120.45	6.566%	$128.3587	$128.36	$128.35	$128.40
7 purchase totals =	$1,050.35		$1,150.8238	$1,150.82	$1,150.85	$1,150.80