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	$173.87	6.871%	$185.8166	$185.82	$185.80	$185.80
Purchase #2	$220.86	11.140%	$245.4638	$245.46	$245.45	$245.50
Purchase #3	$129.38	11.718%	$144.5407	$144.54	$144.55	$144.50
Purchase #4	$112.30	13.615%	$127.5896	$127.59	$127.60	$127.60
Purchase #5	$215.71	12.864%	$243.4589	$243.46	$243.45	$243.50
Purchase #6	$178.79	10.853%	$198.1941	$198.19	$198.20	$198.20
Purchase #7	$247.50	12.633%	$278.7667	$278.77	$278.75	$278.80
7 purchase totals =	$1,278.41		$1,423.8304	$1,423.83	$1,423.80	$1,423.90