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	$25.84	10.431%	$28.5354	$28.54	$28.55	$28.50
Purchase #2	$209.37	13.188%	$236.9817	$236.98	$237.00	$237.00
Purchase #3	$247.34	11.700%	$276.2788	$276.28	$276.30	$276.30
Purchase #4	$57.87	3.390%	$59.8318	$59.83	$59.85	$59.80
Purchase #5	$127.75	10.153%	$140.7205	$140.72	$140.70	$140.70
Purchase #6	$182.70	6.279%	$194.1717	$194.17	$194.15	$194.20
Purchase #7	$39.83	4.565%	$41.6482	$41.65	$41.65	$41.60
7 purchase totals =	$890.70		$978.1681	$978.17	$978.20	$978.10