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	$232.52	11.569%	$259.4202	$259.42	$259.40	$259.40
Purchase #2	$136.29	13.151%	$154.2135	$154.21	$154.20	$154.20
Purchase #3	$137.86	7.310%	$147.9376	$147.94	$147.95	$147.90
Purchase #4	$38.58	10.797%	$42.7455	$42.75	$42.75	$42.70
Purchase #5	$131.46	8.137%	$142.1569	$142.16	$142.15	$142.20
Purchase #6	$223.82	8.153%	$242.068	$242.07	$242.05	$242.10
Purchase #7	$95.47	10.128%	$105.1392	$105.14	$105.15	$105.10
7 purchase totals =	$996.00		$1,093.6809	$1,093.69	$1,093.65	$1,093.60