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	$131.70	13.743%	$149.7995	$149.80	$149.80	$149.80
Purchase #2	$139.55	11.185%	$155.1587	$155.16	$155.15	$155.20
Purchase #3	$57.82	9.141%	$63.1053	$63.11	$63.10	$63.10
Purchase #4	$144.42	13.714%	$164.2258	$164.23	$164.25	$164.20
Purchase #5	$21.51	6.470%	$22.9017	$22.90	$22.90	$22.90
Purchase #6	$51.49	5.167%	$54.1505	$54.15	$54.15	$54.20
Purchase #7	$115.66	7.110%	$123.8834	$123.88	$123.90	$123.90
7 purchase totals =	$662.15		$733.2249	$733.23	$733.25	$733.30