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	$80.40	11.835%	$89.9153	$89.92	$89.90	$89.90
Purchase #2	$14.95	11.222%	$16.6277	$16.63	$16.65	$16.60
Purchase #3	$123.35	11.729%	$137.8177	$137.82	$137.80	$137.80
Purchase #4	$105.86	3.375%	$109.4328	$109.43	$109.45	$109.40
Purchase #5	$138.25	11.489%	$154.1335	$154.13	$154.15	$154.10
Purchase #6	$239.77	13.426%	$271.9615	$271.96	$271.95	$272.00
Purchase #7	$188.59	4.173%	$196.4599	$196.46	$196.45	$196.50
7 purchase totals =	$891.17		$976.3484	$976.35	$976.35	$976.30