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	$102.74	8.171%	$111.1349	$111.13	$111.15	$111.10
Purchase #2	$188.90	8.661%	$205.2606	$205.26	$205.25	$205.30
Purchase #3	$203.90	11.267%	$226.8734	$226.87	$226.85	$226.90
Purchase #4	$57.33	6.610%	$61.1195	$61.12	$61.10	$61.10
Purchase #5	$152.42	10.835%	$168.9347	$168.93	$168.95	$168.90
Purchase #6	$175.90	9.231%	$192.1373	$192.14	$192.15	$192.10
Purchase #7	$120.40	11.821%	$134.6325	$134.63	$134.65	$134.60
7 purchase totals =	$1,001.59		$1,100.0929	$1,100.08	$1,100.10	$1,100.00