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	$228.69	12.841%	$258.0561	$258.06	$258.05	$258.10
Purchase #2	$34.97	6.797%	$37.3469	$37.35	$37.35	$37.30
Purchase #3	$98.38	10.735%	$108.9411	$108.94	$108.95	$108.90
Purchase #4	$36.26	4.507%	$37.8942	$37.89	$37.90	$37.90
Purchase #5	$166.71	5.173%	$175.3339	$175.33	$175.35	$175.30
Purchase #6	$51.60	11.470%	$57.5185	$57.52	$57.50	$57.50
Purchase #7	$56.98	6.210%	$60.5185	$60.52	$60.50	$60.50
7 purchase totals =	$673.59		$735.6092	$735.61	$735.60	$735.50