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	$49.98	13.712%	$56.8333	$56.83	$56.85	$56.80
Purchase #2	$231.47	3.117%	$238.6849	$238.68	$238.70	$238.70
Purchase #3	$78.38	6.280%	$83.3023	$83.30	$83.30	$83.30
Purchase #4	$207.47	12.648%	$233.7108	$233.71	$233.70	$233.70
Purchase #5	$161.87	11.369%	$180.273	$180.27	$180.25	$180.30
Purchase #6	$104.33	7.493%	$112.1474	$112.15	$112.15	$112.10
Purchase #7	$236.96	11.616%	$264.4853	$264.49	$264.50	$264.50
7 purchase totals =	$1,070.46		$1,169.4370	$1,169.43	$1,169.45	$1,169.40