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	$222.33	8.297%	$240.7767	$240.78	$240.80	$240.80
Purchase #2	$176.74	13.663%	$200.888	$200.89	$200.90	$200.90
Purchase #3	$123.95	10.861%	$137.4122	$137.41	$137.40	$137.40
Purchase #4	$21.82	7.726%	$23.5058	$23.51	$23.50	$23.50
Purchase #5	$205.63	6.692%	$219.3908	$219.39	$219.40	$219.40
Purchase #6	$196.54	3.404%	$203.2302	$203.23	$203.25	$203.20
Purchase #7	$61.31	4.837%	$64.2756	$64.28	$64.30	$64.30
7 purchase totals =	$1,008.32		$1,089.4793	$1,089.49	$1,089.55	$1,089.50