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	$7.47	5.270%	$7.8637	$7.86	$7.85	$7.90
Purchase #2	$47.26	11.846%	$52.8584	$52.86	$52.85	$52.90
Purchase #3	$180.43	13.248%	$204.3334	$204.33	$204.35	$204.30
Purchase #4	$131.84	10.848%	$146.142	$146.14	$146.15	$146.10
Purchase #5	$243.43	3.182%	$251.1759	$251.18	$251.20	$251.20
Purchase #6	$66.32	6.469%	$70.6102	$70.61	$70.60	$70.60
Purchase #7	$37.44	7.535%	$40.2611	$40.26	$40.25	$40.30
7 purchase totals =	$714.19		$773.2447	$773.24	$773.25	$773.30