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	$123.89	13.325%	$140.3983	$140.40	$140.40	$140.40
Purchase #2	$6.69	7.787%	$7.211	$7.21	$7.20	$7.20
Purchase #3	$99.59	10.353%	$109.9006	$109.90	$109.90	$109.90
Purchase #4	$25.42	10.265%	$28.0294	$28.03	$28.05	$28.00
Purchase #5	$7.92	8.724%	$8.6109	$8.61	$8.60	$8.60
Purchase #6	$98.51	6.751%	$105.1604	$105.16	$105.15	$105.20
Purchase #7	$239.58	10.171%	$263.9477	$263.95	$263.95	$263.90
7 purchase totals =	$601.60		$663.2583	$663.26	$663.25	$663.20