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	$78.94	5.415%	$83.2146	$83.21	$83.20	$83.20
Purchase #2	$126.35	11.493%	$140.8714	$140.87	$140.85	$140.90
Purchase #3	$78.56	10.140%	$86.526	$86.53	$86.55	$86.50
Purchase #4	$231.53	4.268%	$241.4117	$241.41	$241.40	$241.40
Purchase #5	$61.37	6.394%	$65.294	$65.29	$65.30	$65.30
Purchase #6	$95.76	4.707%	$100.2674	$100.27	$100.25	$100.30
Purchase #7	$70.95	13.596%	$80.5964	$80.60	$80.60	$80.60
7 purchase totals =	$743.46		$798.1815	$798.18	$798.15	$798.20