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	$170.39	10.810%	$188.8092	$188.81	$188.80	$188.80
Purchase #2	$236.88	13.406%	$268.6361	$268.64	$268.65	$268.60
Purchase #3	$96.59	4.189%	$100.6362	$100.64	$100.65	$100.60
Purchase #4	$128.87	10.570%	$142.4916	$142.49	$142.50	$142.50
Purchase #5	$130.65	10.498%	$144.3656	$144.37	$144.35	$144.40
Purchase #6	$174.69	10.300%	$192.6831	$192.68	$192.70	$192.70
Purchase #7	$26.83	13.133%	$30.3536	$30.35	$30.35	$30.40
7 purchase totals =	$964.90		$1,067.9754	$1,067.98	$1,068.00	$1,068.00