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	$141.91	9.182%	$154.9402	$154.94	$154.95	$154.90
Purchase #2	$135.30	11.842%	$151.3222	$151.32	$151.30	$151.30
Purchase #3	$209.46	4.835%	$219.5874	$219.59	$219.60	$219.60
Purchase #4	$58.25	11.430%	$64.908	$64.91	$64.90	$64.90
Purchase #5	$96.64	11.604%	$107.8541	$107.85	$107.85	$107.90
Purchase #6	$40.63	5.532%	$42.8777	$42.88	$42.90	$42.90
Purchase #7	$37.65	13.106%	$42.5844	$42.58	$42.60	$42.60
7 purchase totals =	$719.84		$784.0740	$784.07	$784.10	$784.10