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	$151.56	9.675%	$166.2234	$166.22	$166.20	$166.20
Purchase #2	$157.29	5.639%	$166.1596	$166.16	$166.15	$166.20
Purchase #3	$84.74	13.821%	$96.4519	$96.45	$96.45	$96.50
Purchase #4	$90.56	8.376%	$98.1453	$98.15	$98.15	$98.10
Purchase #5	$115.61	13.396%	$131.0971	$131.10	$131.10	$131.10
Purchase #6	$102.67	13.416%	$116.4442	$116.44	$116.45	$116.40
Purchase #7	$141.93	10.474%	$156.7957	$156.80	$156.80	$156.80
7 purchase totals =	$844.36		$931.3172	$931.32	$931.30	$931.30