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	$70.31	7.841%	$75.823	$75.82	$75.80	$75.80
Purchase #2	$88.97	8.340%	$96.3901	$96.39	$96.40	$96.40
Purchase #3	$43.43	4.715%	$45.4777	$45.48	$45.50	$45.50
Purchase #4	$80.74	11.201%	$89.7837	$89.78	$89.80	$89.80
Purchase #5	$99.67	4.806%	$104.4601	$104.46	$104.45	$104.50
Purchase #6	$23.33	3.184%	$24.0728	$24.07	$24.05	$24.10
Purchase #7	$33.47	10.609%	$37.0208	$37.02	$37.00	$37.00
7 purchase totals =	$439.92		$473.0282	$473.02	$473.00	$473.10