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	$30.67	3.756%	$31.822	$31.82	$31.80	$31.80
Purchase #2	$141.54	8.255%	$153.2241	$153.22	$153.20	$153.20
Purchase #3	$71.30	12.386%	$80.1312	$80.13	$80.15	$80.10
Purchase #4	$216.86	13.186%	$245.4552	$245.46	$245.45	$245.50
Purchase #5	$85.58	11.122%	$95.0982	$95.10	$95.10	$95.10
Purchase #6	$95.71	3.140%	$98.7153	$98.72	$98.70	$98.70
Purchase #7	$67.43	6.688%	$71.9397	$71.94	$71.95	$71.90
7 purchase totals =	$709.09		$776.3857	$776.39	$776.35	$776.30