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	$19.36	13.841%	$22.0396	$22.04	$22.05	$22.00
Purchase #2	$187.90	11.713%	$209.9087	$209.91	$209.90	$209.90
Purchase #3	$172.99	4.765%	$181.233	$181.23	$181.25	$181.20
Purchase #4	$99.45	5.756%	$105.1743	$105.17	$105.15	$105.20
Purchase #5	$237.90	3.222%	$245.5651	$245.57	$245.55	$245.60
Purchase #6	$13.56	11.609%	$15.1342	$15.13	$15.15	$15.10
Purchase #7	$162.40	10.784%	$179.9132	$179.91	$179.90	$179.90
7 purchase totals =	$893.56		$958.9681	$958.96	$958.95	$958.90