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	$106.30	8.783%	$115.6363	$115.64	$115.65	$115.60
Purchase #2	$114.77	4.817%	$120.2985	$120.30	$120.30	$120.30
Purchase #3	$124.65	10.388%	$137.5986	$137.60	$137.60	$137.60
Purchase #4	$52.37	13.287%	$59.3284	$59.33	$59.35	$59.30
Purchase #5	$41.83	8.180%	$45.2517	$45.25	$45.25	$45.30
Purchase #6	$134.71	6.237%	$143.1119	$143.11	$143.10	$143.10
Purchase #7	$29.92	9.704%	$32.8234	$32.82	$32.80	$32.80
7 purchase totals =	$604.55		$654.0488	$654.05	$654.05	$654.00