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	$69.38	13.558%	$78.7865	$78.79	$78.80	$78.80
Purchase #2	$160.39	8.345%	$173.7745	$173.77	$173.75	$173.80
Purchase #3	$65.41	8.746%	$71.1308	$71.13	$71.15	$71.10
Purchase #4	$130.90	11.356%	$145.765	$145.77	$145.75	$145.80
Purchase #5	$103.31	8.768%	$112.3682	$112.37	$112.35	$112.40
Purchase #6	$98.89	4.123%	$102.9672	$102.97	$102.95	$103.00
Purchase #7	$75.36	10.402%	$83.1989	$83.20	$83.20	$83.20
7 purchase totals =	$703.64		$767.9911	$768.00	$767.95	$768.10