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	$77.67	6.558%	$82.7636	$82.76	$82.75	$82.80
Purchase #2	$45.43	13.533%	$51.578	$51.58	$51.60	$51.60
Purchase #3	$96.97	3.222%	$100.0944	$100.09	$100.10	$100.10
Purchase #4	$191.54	12.483%	$215.4499	$215.45	$215.45	$215.40
Purchase #5	$31.71	13.610%	$36.0257	$36.03	$36.05	$36.00
Purchase #6	$94.75	10.461%	$104.6618	$104.66	$104.65	$104.70
Purchase #7	$122.44	7.132%	$131.1724	$131.17	$131.15	$131.20
7 purchase totals =	$660.51		$721.7458	$721.74	$721.75	$721.80