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	$83.67	8.593%	$90.8598	$90.86	$90.85	$90.90
Purchase #2	$82.31	5.678%	$86.9836	$86.98	$87.00	$87.00
Purchase #3	$218.65	11.796%	$244.442	$244.44	$244.45	$244.40
Purchase #4	$96.82	12.689%	$109.1055	$109.11	$109.10	$109.10
Purchase #5	$33.83	12.103%	$37.9244	$37.92	$37.90	$37.90
Purchase #6	$107.36	12.672%	$120.9647	$120.96	$120.95	$121.00
Purchase #7	$248.31	11.247%	$276.2374	$276.24	$276.25	$276.20
7 purchase totals =	$870.95		$966.5174	$966.51	$966.50	$966.50