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	$140.79	11.401%	$156.8415	$156.84	$156.85	$156.80
Purchase #2	$196.94	11.690%	$219.9623	$219.96	$219.95	$220.00
Purchase #3	$230.33	12.291%	$258.6399	$258.64	$258.65	$258.60
Purchase #4	$117.93	5.464%	$124.3737	$124.37	$124.35	$124.40
Purchase #5	$144.26	6.650%	$153.8533	$153.85	$153.85	$153.90
Purchase #6	$90.90	10.605%	$100.5399	$100.54	$100.55	$100.50
Purchase #7	$24.42	12.356%	$27.4373	$27.44	$27.45	$27.40
7 purchase totals =	$945.57		$1,041.6479	$1,041.64	$1,041.65	$1,041.60