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	$154.31	12.352%	$173.3704	$173.37	$173.35	$173.40
Purchase #2	$127.46	11.557%	$142.1906	$142.19	$142.20	$142.20
Purchase #3	$32.92	13.269%	$37.2882	$37.29	$37.30	$37.30
Purchase #4	$244.29	5.573%	$257.9043	$257.90	$257.90	$257.90
Purchase #5	$19.44	8.651%	$21.1218	$21.12	$21.10	$21.10
Purchase #6	$193.81	9.851%	$212.9022	$212.90	$212.90	$212.90
Purchase #7	$44.37	3.795%	$46.0538	$46.05	$46.05	$46.10
7 purchase totals =	$816.60		$890.8313	$890.82	$890.80	$890.90