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	$204.78	9.189%	$223.5972	$223.60	$223.60	$223.60
Purchase #2	$156.25	10.289%	$172.3266	$172.33	$172.35	$172.30
Purchase #3	$51.84	13.317%	$58.7435	$58.74	$58.75	$58.70
Purchase #4	$66.97	9.769%	$73.5123	$73.51	$73.50	$73.50
Purchase #5	$58.43	13.847%	$66.5208	$66.52	$66.50	$66.50
Purchase #6	$38.72	10.474%	$42.7755	$42.78	$42.80	$42.80
Purchase #7	$170.75	12.366%	$191.8649	$191.86	$191.85	$191.90
7 purchase totals =	$747.74		$829.3408	$829.34	$829.35	$829.30