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	$109.54	12.839%	$123.6038	$123.60	$123.60	$123.60
Purchase #2	$100.27	9.446%	$109.7415	$109.74	$109.75	$109.70
Purchase #3	$69.77	11.711%	$77.9408	$77.94	$77.95	$77.90
Purchase #4	$234.90	6.471%	$250.1004	$250.10	$250.10	$250.10
Purchase #5	$40.35	4.108%	$42.0076	$42.01	$42.00	$42.00
Purchase #6	$75.85	13.457%	$86.0571	$86.06	$86.05	$86.10
Purchase #7	$41.38	11.539%	$46.1548	$46.15	$46.15	$46.20
7 purchase totals =	$672.06		$735.6060	$735.60	$735.60	$735.60