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	$81.27	12.712%	$91.601	$91.60	$91.60	$91.60
Purchase #2	$89.28	7.406%	$95.8921	$95.89	$95.90	$95.90
Purchase #3	$146.53	3.199%	$151.2175	$151.22	$151.20	$151.20
Purchase #4	$74.88	9.825%	$82.237	$82.24	$82.25	$82.20
Purchase #5	$192.63	6.781%	$205.6922	$205.69	$205.70	$205.70
Purchase #6	$50.51	4.583%	$52.8249	$52.82	$52.80	$52.80
Purchase #7	$152.88	6.208%	$162.3708	$162.37	$162.35	$162.40
7 purchase totals =	$787.98		$841.8355	$841.83	$841.80	$841.80