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	$146.25	12.848%	$165.0402	$165.04	$165.05	$165.00
Purchase #2	$196.91	6.378%	$209.4689	$209.47	$209.45	$209.50
Purchase #3	$234.70	13.672%	$266.7882	$266.79	$266.80	$266.80
Purchase #4	$76.56	9.221%	$83.6196	$83.62	$83.60	$83.60
Purchase #5	$53.43	10.788%	$59.194	$59.19	$59.20	$59.20
Purchase #6	$155.99	4.155%	$162.4714	$162.47	$162.45	$162.50
Purchase #7	$113.71	5.753%	$120.2517	$120.25	$120.25	$120.30
7 purchase totals =	$977.55		$1,066.8340	$1,066.83	$1,066.80	$1,066.90