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	$166.82	3.329%	$172.3734	$172.37	$172.35	$172.40
Purchase #2	$198.96	9.395%	$217.6523	$217.65	$217.65	$217.70
Purchase #3	$75.81	3.495%	$78.4596	$78.46	$78.45	$78.50
Purchase #4	$204.45	11.187%	$227.3218	$227.32	$227.30	$227.30
Purchase #5	$42.38	11.822%	$47.3902	$47.39	$47.40	$47.40
Purchase #6	$213.92	4.343%	$223.2105	$223.21	$223.20	$223.20
Purchase #7	$30.29	9.135%	$33.057	$33.06	$33.05	$33.10
7 purchase totals =	$932.63		$999.4648	$999.46	$999.40	$999.60