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	$243.78	4.776%	$255.4229	$255.42	$255.40	$255.40
Purchase #2	$141.37	6.780%	$150.9549	$150.95	$150.95	$151.00
Purchase #3	$82.30	7.659%	$88.6034	$88.60	$88.60	$88.60
Purchase #4	$139.60	5.451%	$147.2096	$147.21	$147.20	$147.20
Purchase #5	$133.26	8.483%	$144.5644	$144.56	$144.55	$144.60
Purchase #6	$41.61	8.717%	$45.2371	$45.24	$45.25	$45.20
Purchase #7	$118.39	8.184%	$128.079	$128.08	$128.10	$128.10
7 purchase totals =	$900.31		$960.0713	$960.06	$960.05	$960.10