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	$51.57	3.718%	$53.4874	$53.49	$53.50	$53.50
Purchase #2	$211.44	10.312%	$233.2437	$233.24	$233.25	$233.20
Purchase #3	$118.42	4.373%	$123.5985	$123.60	$123.60	$123.60
Purchase #4	$78.45	12.558%	$88.3018	$88.30	$88.30	$88.30
Purchase #5	$116.29	12.543%	$130.8763	$130.88	$130.90	$130.90
Purchase #6	$96.38	6.407%	$102.5551	$102.56	$102.55	$102.60
Purchase #7	$177.70	7.302%	$190.6757	$190.68	$190.70	$190.70
7 purchase totals =	$850.25		$922.7385	$922.75	$922.80	$922.80