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	$146.80	7.113%	$157.2419	$157.24	$157.25	$157.20
Purchase #2	$154.43	6.609%	$164.6363	$164.64	$164.65	$164.60
Purchase #3	$130.41	12.350%	$146.5156	$146.52	$146.50	$146.50
Purchase #4	$139.52	12.382%	$156.7954	$156.80	$156.80	$156.80
Purchase #5	$37.89	8.569%	$41.1368	$41.14	$41.15	$41.10
Purchase #6	$52.35	3.413%	$54.1367	$54.14	$54.15	$54.10
Purchase #7	$107.75	8.147%	$116.5284	$116.53	$116.55	$116.50
7 purchase totals =	$769.15		$836.9911	$837.01	$837.05	$836.80