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	$42.64	10.179%	$46.9803	$46.98	$47.00	$47.00
Purchase #2	$186.71	11.304%	$207.8157	$207.82	$207.80	$207.80
Purchase #3	$19.29	13.152%	$21.827	$21.83	$21.85	$21.80
Purchase #4	$18.60	12.277%	$20.8835	$20.88	$20.90	$20.90
Purchase #5	$41.88	4.541%	$43.7818	$43.78	$43.80	$43.80
Purchase #6	$74.43	5.623%	$78.6152	$78.62	$78.60	$78.60
Purchase #7	$72.65	9.738%	$79.7247	$79.72	$79.70	$79.70
7 purchase totals =	$456.20		$499.6282	$499.63	$499.65	$499.60