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	$167.32	13.478%	$189.8714	$189.87	$189.85	$189.90
Purchase #2	$207.35	6.594%	$221.0227	$221.02	$221.00	$221.00
Purchase #3	$132.55	10.398%	$146.3325	$146.33	$146.35	$146.30
Purchase #4	$19.96	4.512%	$20.8606	$20.86	$20.85	$20.90
Purchase #5	$40.33	6.300%	$42.8708	$42.87	$42.85	$42.90
Purchase #6	$134.64	7.178%	$144.3045	$144.30	$144.30	$144.30
Purchase #7	$147.95	3.455%	$153.0617	$153.06	$153.05	$153.10
7 purchase totals =	$850.10		$918.3242	$918.31	$918.25	$918.40