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	$40.96	3.524%	$42.4034	$42.40	$42.40	$42.40
Purchase #2	$248.76	13.612%	$282.6212	$282.62	$282.60	$282.60
Purchase #3	$39.79	4.150%	$41.4413	$41.44	$41.45	$41.40
Purchase #4	$249.28	10.847%	$276.3194	$276.32	$276.30	$276.30
Purchase #5	$99.62	12.164%	$111.7378	$111.74	$111.75	$111.70
Purchase #6	$203.33	7.732%	$219.0515	$219.05	$219.05	$219.10
Purchase #7	$146.85	9.206%	$160.369	$160.37	$160.35	$160.40
7 purchase totals =	$1,028.59		$1,133.9436	$1,133.94	$1,133.90	$1,133.90