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	$117.39	10.203%	$129.3673	$129.37	$129.35	$129.40
Purchase #2	$150.68	13.657%	$171.2584	$171.26	$171.25	$171.30
Purchase #3	$69.81	10.109%	$76.8671	$76.87	$76.85	$76.90
Purchase #4	$90.98	4.710%	$95.2652	$95.27	$95.25	$95.30
Purchase #5	$172.41	7.658%	$185.6132	$185.61	$185.60	$185.60
Purchase #6	$64.54	4.589%	$67.5017	$67.50	$67.50	$67.50
Purchase #7	$90.34	8.565%	$98.0776	$98.08	$98.10	$98.10
7 purchase totals =	$756.15		$823.9505	$823.96	$823.90	$824.10