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	$61.84	7.152%	$66.2628	$66.26	$66.25	$66.30
Purchase #2	$154.74	12.648%	$174.3115	$174.31	$174.30	$174.30
Purchase #3	$74.46	5.767%	$78.7541	$78.75	$78.75	$78.80
Purchase #4	$150.44	5.438%	$158.6209	$158.62	$158.60	$158.60
Purchase #5	$233.38	13.627%	$265.1827	$265.18	$265.20	$265.20
Purchase #6	$76.34	7.687%	$82.2083	$82.21	$82.20	$82.20
Purchase #7	$90.35	13.635%	$102.6692	$102.67	$102.65	$102.70
7 purchase totals =	$841.55		$928.0095	$928.00	$927.95	$928.10