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	$41.72	4.278%	$43.5048	$43.50	$43.50	$43.50
Purchase #2	$134.69	7.421%	$144.6853	$144.69	$144.70	$144.70
Purchase #3	$65.47	9.565%	$71.7322	$71.73	$71.75	$71.70
Purchase #4	$46.72	7.731%	$50.3319	$50.33	$50.35	$50.30
Purchase #5	$197.84	5.336%	$208.3967	$208.40	$208.40	$208.40
Purchase #6	$223.79	13.317%	$253.5921	$253.59	$253.60	$253.60
Purchase #7	$87.65	13.479%	$99.4643	$99.46	$99.45	$99.50
7 purchase totals =	$797.88		$871.7073	$871.70	$871.75	$871.70