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	$170.51	4.226%	$177.7158	$177.72	$177.70	$177.70
Purchase #2	$91.99	4.426%	$96.0615	$96.06	$96.05	$96.10
Purchase #3	$239.55	12.236%	$268.8613	$268.86	$268.85	$268.90
Purchase #4	$245.72	13.476%	$278.8332	$278.83	$278.85	$278.80
Purchase #5	$67.51	6.750%	$72.0669	$72.07	$72.05	$72.10
Purchase #6	$90.64	13.660%	$103.0214	$103.02	$103.00	$103.00
Purchase #7	$38.86	7.131%	$41.6311	$41.63	$41.65	$41.60
7 purchase totals =	$944.78		$1,038.1912	$1,038.19	$1,038.15	$1,038.20