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	$160.30	11.218%	$178.2825	$178.28	$178.30	$178.30
Purchase #2	$166.73	11.581%	$186.039	$186.04	$186.05	$186.00
Purchase #3	$241.84	10.832%	$268.0361	$268.04	$268.05	$268.00
Purchase #4	$33.32	9.173%	$36.3764	$36.38	$36.40	$36.40
Purchase #5	$13.28	11.847%	$14.8533	$14.85	$14.85	$14.90
Purchase #6	$38.35	5.330%	$40.3941	$40.39	$40.40	$40.40
Purchase #7	$156.51	10.147%	$172.3911	$172.39	$172.40	$172.40
7 purchase totals =	$810.33		$896.3725	$896.37	$896.45	$896.40