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	$166.36	11.280%	$185.1254	$185.13	$185.15	$185.10
Purchase #2	$142.35	13.862%	$162.0826	$162.08	$162.10	$162.10
Purchase #3	$173.47	4.188%	$180.7349	$180.73	$180.75	$180.70
Purchase #4	$95.41	5.196%	$100.3675	$100.37	$100.35	$100.40
Purchase #5	$241.31	12.495%	$271.4617	$271.46	$271.45	$271.50
Purchase #6	$174.46	10.595%	$192.944	$192.94	$192.95	$192.90
Purchase #7	$98.58	13.814%	$112.1978	$112.20	$112.20	$112.20
7 purchase totals =	$1,091.94		$1,204.9139	$1,204.91	$1,204.95	$1,204.90