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	$75.40	4.551%	$78.8315	$78.83	$78.85	$78.80
Purchase #2	$99.41	9.504%	$108.8579	$108.86	$108.85	$108.90
Purchase #3	$125.46	12.662%	$141.3457	$141.35	$141.35	$141.30
Purchase #4	$81.34	11.142%	$90.4029	$90.40	$90.40	$90.40
Purchase #5	$67.95	5.385%	$71.6091	$71.61	$71.60	$71.60
Purchase #6	$42.63	4.532%	$44.562	$44.56	$44.55	$44.60
Purchase #7	$111.93	6.658%	$119.3823	$119.38	$119.40	$119.40
7 purchase totals =	$604.12		$654.9914	$654.99	$655.00	$655.00