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	$122.92	13.139%	$139.0705	$139.07	$139.05	$139.10
Purchase #2	$235.25	12.347%	$264.2963	$264.30	$264.30	$264.30
Purchase #3	$19.60	3.174%	$20.2221	$20.22	$20.20	$20.20
Purchase #4	$37.76	8.302%	$40.8948	$40.89	$40.90	$40.90
Purchase #5	$19.92	4.564%	$20.8291	$20.83	$20.85	$20.80
Purchase #6	$53.42	7.734%	$57.5515	$57.55	$57.55	$57.60
Purchase #7	$176.68	7.645%	$190.1872	$190.19	$190.20	$190.20
7 purchase totals =	$665.55		$733.0515	$733.05	$733.05	$733.10