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	$35.49	10.180%	$39.1029	$39.10	$39.10	$39.10
Purchase #2	$244.79	3.648%	$253.7199	$253.72	$253.70	$253.70
Purchase #3	$84.69	10.140%	$93.2776	$93.28	$93.30	$93.30
Purchase #4	$122.77	4.117%	$127.8244	$127.82	$127.80	$127.80
Purchase #5	$159.64	4.541%	$166.8893	$166.89	$166.90	$166.90
Purchase #6	$198.72	6.656%	$211.9468	$211.95	$211.95	$211.90
Purchase #7	$95.97	8.139%	$103.781	$103.78	$103.80	$103.80
7 purchase totals =	$942.07		$996.5419	$996.54	$996.55	$996.50