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	$72.46	7.367%	$77.7981	$77.80	$77.80	$77.80
Purchase #2	$211.30	6.787%	$225.6409	$225.64	$225.65	$225.60
Purchase #3	$113.44	12.340%	$127.4385	$127.44	$127.45	$127.40
Purchase #4	$85.27	4.532%	$89.1344	$89.13	$89.15	$89.10
Purchase #5	$229.84	8.726%	$249.8958	$249.90	$249.90	$249.90
Purchase #6	$237.55	9.242%	$259.5044	$259.50	$259.50	$259.50
Purchase #7	$62.36	8.506%	$67.6643	$67.66	$67.65	$67.70
7 purchase totals =	$1,012.22		$1,097.0764	$1,097.07	$1,097.10	$1,097.00