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	$101.45	4.465%	$105.9797	$105.98	$106.00	$106.00
Purchase #2	$231.84	13.688%	$263.5743	$263.57	$263.55	$263.60
Purchase #3	$64.98	3.528%	$67.2725	$67.27	$67.25	$67.30
Purchase #4	$111.55	6.738%	$119.0662	$119.07	$119.05	$119.10
Purchase #5	$72.99	9.735%	$80.0956	$80.10	$80.10	$80.10
Purchase #6	$146.91	13.113%	$166.1743	$166.17	$166.15	$166.20
Purchase #7	$19.34	4.811%	$20.2704	$20.27	$20.25	$20.30
7 purchase totals =	$749.06		$822.4330	$822.43	$822.35	$822.60