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	$178.74	3.301%	$184.6402	$184.64	$184.65	$184.60
Purchase #2	$167.51	7.169%	$179.5188	$179.52	$179.50	$179.50
Purchase #3	$86.91	5.532%	$91.7179	$91.72	$91.70	$91.70
Purchase #4	$78.38	7.104%	$83.9481	$83.95	$83.95	$83.90
Purchase #5	$144.55	7.330%	$155.1455	$155.15	$155.15	$155.10
Purchase #6	$123.79	3.818%	$128.5163	$128.52	$128.50	$128.50
Purchase #7	$196.49	5.792%	$207.8707	$207.87	$207.85	$207.90
7 purchase totals =	$976.37		$1,031.3575	$1,031.37	$1,031.30	$1,031.20