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	$33.48	13.151%	$37.883	$37.88	$37.90	$37.90
Purchase #2	$151.43	6.497%	$161.2684	$161.27	$161.25	$161.30
Purchase #3	$93.62	4.483%	$97.817	$97.82	$97.80	$97.80
Purchase #4	$96.46	5.779%	$102.0344	$102.03	$102.05	$102.00
Purchase #5	$159.41	5.142%	$167.6069	$167.61	$167.60	$167.60
Purchase #6	$48.81	6.807%	$52.1325	$52.13	$52.15	$52.10
Purchase #7	$96.97	12.553%	$109.1426	$109.14	$109.15	$109.10
7 purchase totals =	$680.18		$727.8848	$727.88	$727.90	$727.80