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	$39.96	5.578%	$42.189	$42.19	$42.20	$42.20
Purchase #2	$153.81	12.871%	$173.6069	$173.61	$173.60	$173.60
Purchase #3	$41.33	6.710%	$44.1032	$44.10	$44.10	$44.10
Purchase #4	$62.96	4.687%	$65.9109	$65.91	$65.90	$65.90
Purchase #5	$6.26	10.228%	$6.9003	$6.90	$6.90	$6.90
Purchase #6	$228.41	5.276%	$240.4609	$240.46	$240.45	$240.50
Purchase #7	$168.39	11.642%	$187.994	$187.99	$188.00	$188.00
7 purchase totals =	$701.12		$761.1652	$761.16	$761.15	$761.20