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	$11.61	5.742%	$12.2766	$12.28	$12.30	$12.30
Purchase #2	$77.72	13.333%	$88.0824	$88.08	$88.10	$88.10
Purchase #3	$125.85	13.333%	$142.6296	$142.63	$142.65	$142.60
Purchase #4	$236.93	11.808%	$264.9067	$264.91	$264.90	$264.90
Purchase #5	$181.80	6.728%	$194.0315	$194.03	$194.05	$194.00
Purchase #6	$51.79	4.803%	$54.2775	$54.28	$54.30	$54.30
Purchase #7	$98.32	7.627%	$105.8189	$105.82	$105.80	$105.80
7 purchase totals =	$784.02		$862.0232	$862.03	$862.10	$862.00