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	$95.41	4.591%	$99.7903	$99.79	$99.80	$99.80
Purchase #2	$98.65	9.192%	$107.7179	$107.72	$107.70	$107.70
Purchase #3	$64.40	9.189%	$70.3177	$70.32	$70.30	$70.30
Purchase #4	$126.40	12.649%	$142.3883	$142.39	$142.40	$142.40
Purchase #5	$55.67	6.520%	$59.2997	$59.30	$59.30	$59.30
Purchase #6	$58.66	10.199%	$64.6427	$64.64	$64.65	$64.60
Purchase #7	$145.90	13.243%	$165.2215	$165.22	$165.20	$165.20
7 purchase totals =	$645.09		$709.3781	$709.38	$709.35	$709.30