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	$82.39	9.751%	$90.4238	$90.42	$90.40	$90.40
Purchase #2	$44.49	4.593%	$46.5334	$46.53	$46.55	$46.50
Purchase #3	$17.39	5.650%	$18.3725	$18.37	$18.35	$18.40
Purchase #4	$141.96	7.317%	$152.3472	$152.35	$152.35	$152.30
Purchase #5	$115.25	7.529%	$123.9272	$123.93	$123.95	$123.90
Purchase #6	$124.33	8.809%	$135.2822	$135.28	$135.30	$135.30
Purchase #7	$162.86	5.329%	$171.5388	$171.54	$171.55	$171.50
7 purchase totals =	$688.67		$738.4251	$738.42	$738.45	$738.30