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	$82.28	9.806%	$90.3484	$90.35	$90.35	$90.30
Purchase #2	$145.62	3.215%	$150.3017	$150.30	$150.30	$150.30
Purchase #3	$194.38	9.767%	$213.3651	$213.37	$213.35	$213.40
Purchase #4	$15.95	7.455%	$17.1391	$17.14	$17.15	$17.10
Purchase #5	$172.96	3.150%	$178.4082	$178.41	$178.40	$178.40
Purchase #6	$59.87	8.656%	$65.0523	$65.05	$65.05	$65.10
Purchase #7	$77.66	13.811%	$88.3856	$88.39	$88.40	$88.40
7 purchase totals =	$748.72		$803.0004	$803.01	$803.00	$803.00