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	$142.70	4.428%	$149.0188	$149.02	$149.00	$149.00
Purchase #2	$114.51	3.526%	$118.5476	$118.55	$118.55	$118.50
Purchase #3	$124.83	6.765%	$133.2747	$133.27	$133.25	$133.30
Purchase #4	$80.35	13.561%	$91.2463	$91.25	$91.25	$91.20
Purchase #5	$152.60	12.480%	$171.6445	$171.64	$171.65	$171.60
Purchase #6	$63.91	11.333%	$71.1529	$71.15	$71.15	$71.20
Purchase #7	$168.66	13.587%	$191.5758	$191.58	$191.60	$191.60
7 purchase totals =	$847.56		$926.4606	$926.46	$926.45	$926.40