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	$63.41	10.647%	$70.1613	$70.16	$70.15	$70.20
Purchase #2	$144.98	4.512%	$151.5215	$151.52	$151.50	$151.50
Purchase #3	$82.63	4.138%	$86.0492	$86.05	$86.05	$86.00
Purchase #4	$203.52	9.141%	$222.1238	$222.12	$222.10	$222.10
Purchase #5	$120.62	11.852%	$134.9159	$134.92	$134.90	$134.90
Purchase #6	$78.98	11.557%	$88.1077	$88.11	$88.10	$88.10
Purchase #7	$73.77	12.689%	$83.1307	$83.13	$83.15	$83.10
7 purchase totals =	$767.91		$836.0101	$836.01	$835.95	$835.90