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	$188.91	12.461%	$212.4501	$212.45	$212.45	$212.50
Purchase #2	$123.61	4.716%	$129.4394	$129.44	$129.45	$129.40
Purchase #3	$73.92	6.134%	$78.4543	$78.45	$78.45	$78.50
Purchase #4	$170.31	5.246%	$179.2445	$179.24	$179.25	$179.20
Purchase #5	$198.81	11.743%	$222.1563	$222.16	$222.15	$222.20
Purchase #6	$198.41	10.337%	$218.9196	$218.92	$218.90	$218.90
Purchase #7	$141.30	3.171%	$145.7806	$145.78	$145.80	$145.80
7 purchase totals =	$1,095.27		$1,186.4448	$1,186.44	$1,186.45	$1,186.50