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	$45.69	10.419%	$50.4504	$50.45	$50.45	$50.50
Purchase #2	$180.70	9.612%	$198.0689	$198.07	$198.05	$198.10
Purchase #3	$32.46	12.793%	$36.6126	$36.61	$36.60	$36.60
Purchase #4	$17.94	3.867%	$18.6337	$18.63	$18.65	$18.60
Purchase #5	$100.25	11.562%	$111.8409	$111.84	$111.85	$111.80
Purchase #6	$94.43	10.410%	$104.2602	$104.26	$104.25	$104.30
Purchase #7	$215.58	5.621%	$227.6978	$227.70	$227.70	$227.70
7 purchase totals =	$687.05		$747.5645	$747.56	$747.55	$747.60