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	$94.56	5.544%	$99.8024	$99.80	$99.80	$99.80
Purchase #2	$48.71	6.383%	$51.8192	$51.82	$51.80	$51.80
Purchase #3	$64.25	9.246%	$70.1906	$70.19	$70.20	$70.20
Purchase #4	$112.94	5.148%	$118.7542	$118.75	$118.75	$118.80
Purchase #5	$167.55	12.748%	$188.9093	$188.91	$188.90	$188.90
Purchase #6	$146.27	13.663%	$166.2549	$166.25	$166.25	$166.30
Purchase #7	$84.49	13.301%	$95.728	$95.73	$95.75	$95.70
7 purchase totals =	$718.77		$791.4586	$791.45	$791.45	$791.50