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	$41.92	13.842%	$47.7226	$47.72	$47.70	$47.70
Purchase #2	$38.91	6.381%	$41.3928	$41.39	$41.40	$41.40
Purchase #3	$156.84	13.525%	$178.0526	$178.05	$178.05	$178.10
Purchase #4	$248.38	4.230%	$258.8865	$258.89	$258.90	$258.90
Purchase #5	$152.88	4.150%	$159.2245	$159.22	$159.20	$159.20
Purchase #6	$144.63	9.521%	$158.4002	$158.40	$158.40	$158.40
Purchase #7	$249.54	9.706%	$273.7604	$273.76	$273.75	$273.80
7 purchase totals =	$1,033.10		$1,117.4396	$1,117.43	$1,117.40	$1,117.50