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	$98.93	4.716%	$103.5955	$103.60	$103.60	$103.60
Purchase #2	$37.62	12.165%	$42.1965	$42.20	$42.20	$42.20
Purchase #3	$165.94	11.449%	$184.9385	$184.94	$184.95	$184.90
Purchase #4	$104.58	6.291%	$111.1591	$111.16	$111.15	$111.20
Purchase #5	$127.61	7.810%	$137.5763	$137.58	$137.60	$137.60
Purchase #6	$92.71	13.154%	$104.9051	$104.91	$104.90	$104.90
Purchase #7	$100.86	9.492%	$110.4336	$110.43	$110.45	$110.40
7 purchase totals =	$728.25		$794.8046	$794.82	$794.85	$794.80