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	$158.91	12.164%	$178.2398	$178.24	$178.25	$178.20
Purchase #2	$68.27	9.727%	$74.9106	$74.91	$74.90	$74.90
Purchase #3	$120.32	11.580%	$134.2531	$134.25	$134.25	$134.30
Purchase #4	$152.70	10.630%	$168.932	$168.93	$168.95	$168.90
Purchase #5	$52.44	13.194%	$59.3589	$59.36	$59.35	$59.40
Purchase #6	$109.58	10.344%	$120.915	$120.92	$120.90	$120.90
Purchase #7	$109.50	7.321%	$117.5165	$117.52	$117.50	$117.50
7 purchase totals =	$771.72		$854.1259	$854.13	$854.10	$854.10