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	$91.96	11.374%	$102.4195	$102.42	$102.40	$102.40
Purchase #2	$76.83	8.226%	$83.15	$83.15	$83.15	$83.20
Purchase #3	$6.69	7.277%	$7.1768	$7.18	$7.20	$7.20
Purchase #4	$128.62	12.324%	$144.4711	$144.47	$144.45	$144.50
Purchase #5	$20.62	6.855%	$22.0335	$22.03	$22.05	$22.00
Purchase #6	$73.37	6.799%	$78.3584	$78.36	$78.35	$78.40
Purchase #7	$12.77	13.454%	$14.4881	$14.49	$14.50	$14.50
7 purchase totals =	$410.86		$452.0974	$452.10	$452.10	$452.20