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	$97.28	13.263%	$110.1822	$110.18	$110.20	$110.20
Purchase #2	$200.79	10.720%	$222.3147	$222.31	$222.30	$222.30
Purchase #3	$67.92	6.395%	$72.2635	$72.26	$72.25	$72.30
Purchase #4	$161.55	12.800%	$182.2284	$182.23	$182.25	$182.20
Purchase #5	$28.86	10.296%	$31.8314	$31.83	$31.85	$31.80
Purchase #6	$50.86	7.814%	$54.8342	$54.83	$54.85	$54.80
Purchase #7	$122.27	9.646%	$134.0642	$134.06	$134.05	$134.10
7 purchase totals =	$729.53		$807.7186	$807.70	$807.75	$807.70