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	$233.56	13.829%	$265.859	$265.86	$265.85	$265.90
Purchase #2	$90.25	8.245%	$97.6911	$97.69	$97.70	$97.70
Purchase #3	$30.88	4.353%	$32.2242	$32.22	$32.20	$32.20
Purchase #4	$159.37	10.253%	$175.7102	$175.71	$175.70	$175.70
Purchase #5	$164.38	7.263%	$176.3189	$176.32	$176.30	$176.30
Purchase #6	$59.31	3.227%	$61.2239	$61.22	$61.20	$61.20
Purchase #7	$86.88	3.530%	$89.9469	$89.95	$89.95	$89.90
7 purchase totals =	$824.63		$898.9742	$898.97	$898.90	$898.90