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	$65.44	12.870%	$73.8621	$73.86	$73.85	$73.90
Purchase #2	$178.33	7.463%	$191.6388	$191.64	$191.65	$191.60
Purchase #3	$153.94	7.632%	$165.6887	$165.69	$165.70	$165.70
Purchase #4	$54.61	4.572%	$57.1068	$57.11	$57.10	$57.10
Purchase #5	$92.94	7.357%	$99.7776	$99.78	$99.80	$99.80
Purchase #6	$204.83	7.692%	$220.5855	$220.59	$220.60	$220.60
Purchase #7	$65.51	10.193%	$72.1874	$72.19	$72.20	$72.20
7 purchase totals =	$815.60		$880.8469	$880.86	$880.90	$880.90