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	$170.65	12.209%	$191.4847	$191.48	$191.50	$191.50
Purchase #2	$167.49	10.801%	$185.5806	$185.58	$185.60	$185.60
Purchase #3	$138.87	5.752%	$146.8578	$146.86	$146.85	$146.90
Purchase #4	$234.34	12.804%	$264.3449	$264.34	$264.35	$264.30
Purchase #5	$242.97	10.281%	$267.9497	$267.95	$267.95	$267.90
Purchase #6	$186.34	5.595%	$196.7657	$196.77	$196.75	$196.80
Purchase #7	$38.41	13.799%	$43.7102	$43.71	$43.70	$43.70
7 purchase totals =	$1,179.07		$1,296.6936	$1,296.69	$1,296.70	$1,296.70