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	$43.58	4.159%	$45.3925	$45.39	$45.40	$45.40
Purchase #2	$209.92	11.736%	$234.5562	$234.56	$234.55	$234.60
Purchase #3	$96.70	8.532%	$104.9504	$104.95	$104.95	$105.00
Purchase #4	$76.29	8.139%	$82.4992	$82.50	$82.50	$82.50
Purchase #5	$150.64	4.778%	$157.8376	$157.84	$157.85	$157.80
Purchase #6	$138.96	9.341%	$151.9403	$151.94	$151.95	$151.90
Purchase #7	$6.84	5.566%	$7.2207	$7.22	$7.20	$7.20
7 purchase totals =	$722.93		$784.3969	$784.40	$784.40	$784.40