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	$95.64	13.467%	$108.5198	$108.52	$108.50	$108.50
Purchase #2	$114.46	3.216%	$118.141	$118.14	$118.15	$118.10
Purchase #3	$117.83	8.621%	$127.9881	$127.99	$128.00	$128.00
Purchase #4	$62.98	13.547%	$71.5119	$71.51	$71.50	$71.50
Purchase #5	$72.27	9.851%	$79.3893	$79.39	$79.40	$79.40
Purchase #6	$19.31	3.768%	$20.0376	$20.04	$20.05	$20.00
Purchase #7	$113.37	10.381%	$125.1389	$125.14	$125.15	$125.10
7 purchase totals =	$595.86		$650.7266	$650.73	$650.75	$650.60