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	$168.73	6.688%	$180.0147	$180.01	$180.00	$180.00
Purchase #2	$93.34	4.467%	$97.5095	$97.51	$97.50	$97.50
Purchase #3	$194.93	12.121%	$218.5575	$218.56	$218.55	$218.60
Purchase #4	$37.72	6.632%	$40.2216	$40.22	$40.20	$40.20
Purchase #5	$138.56	11.870%	$155.0071	$155.01	$155.00	$155.00
Purchase #6	$153.70	13.769%	$174.863	$174.86	$174.85	$174.90
Purchase #7	$96.99	8.521%	$105.2545	$105.25	$105.25	$105.30
7 purchase totals =	$883.97		$971.4279	$971.42	$971.35	$971.50