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	$150.99	13.819%	$171.8553	$171.86	$171.85	$171.90
Purchase #2	$151.84	5.411%	$160.0561	$160.06	$160.05	$160.10
Purchase #3	$225.25	9.715%	$247.133	$247.13	$247.15	$247.10
Purchase #4	$152.92	12.503%	$172.0396	$172.04	$172.05	$172.00
Purchase #5	$77.62	9.805%	$85.2306	$85.23	$85.25	$85.20
Purchase #6	$59.87	6.270%	$63.6238	$63.62	$63.60	$63.60
Purchase #7	$97.78	4.608%	$102.2857	$102.29	$102.30	$102.30
7 purchase totals =	$916.27		$1,002.2241	$1,002.23	$1,002.25	$1,002.20