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	$20.94	10.554%	$23.15	$23.15	$23.15	$23.20
Purchase #2	$19.25	5.460%	$20.3011	$20.30	$20.30	$20.30
Purchase #3	$63.72	13.642%	$72.4127	$72.41	$72.40	$72.40
Purchase #4	$39.81	7.715%	$42.8813	$42.88	$42.90	$42.90
Purchase #5	$120.57	10.115%	$132.7657	$132.77	$132.75	$132.80
Purchase #6	$229.58	9.452%	$251.2799	$251.28	$251.30	$251.30
Purchase #7	$129.80	9.782%	$142.497	$142.50	$142.50	$142.50
7 purchase totals =	$623.67		$685.2877	$685.29	$685.30	$685.40