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	$49.55	4.814%	$51.9353	$51.94	$51.95	$51.90
Purchase #2	$78.85	3.777%	$81.8282	$81.83	$81.85	$81.80
Purchase #3	$134.76	12.538%	$151.6562	$151.66	$151.65	$151.70
Purchase #4	$90.71	3.224%	$93.6345	$93.63	$93.65	$93.60
Purchase #5	$37.92	11.477%	$42.2721	$42.27	$42.25	$42.30
Purchase #6	$17.32	6.339%	$18.4179	$18.42	$18.40	$18.40
Purchase #7	$235.89	6.520%	$251.27	$251.27	$251.25	$251.30
7 purchase totals =	$645.00		$691.0142	$691.02	$691.00	$691.00