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	$34.31	12.632%	$38.644	$38.64	$38.65	$38.60
Purchase #2	$250.53	4.629%	$262.127	$262.13	$262.15	$262.10
Purchase #3	$22.79	4.549%	$23.8267	$23.83	$23.85	$23.80
Purchase #4	$132.53	7.788%	$142.8514	$142.85	$142.85	$142.90
Purchase #5	$153.65	4.686%	$160.85	$160.85	$160.85	$160.90
Purchase #6	$59.63	3.355%	$61.6306	$61.63	$61.65	$61.60
Purchase #7	$77.92	11.543%	$86.9143	$86.91	$86.90	$86.90
7 purchase totals =	$731.36		$776.8440	$776.84	$776.90	$776.80