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	$228.33	6.633%	$243.4751	$243.48	$243.50	$243.50
Purchase #2	$173.91	9.325%	$190.1271	$190.13	$190.15	$190.10
Purchase #3	$216.39	6.742%	$230.979	$230.98	$231.00	$231.00
Purchase #4	$167.88	13.323%	$190.2467	$190.25	$190.25	$190.20
Purchase #5	$78.94	4.864%	$82.7796	$82.78	$82.80	$82.80
Purchase #6	$162.31	10.535%	$179.4094	$179.41	$179.40	$179.40
Purchase #7	$215.45	12.828%	$243.0879	$243.09	$243.10	$243.10
7 purchase totals =	$1,243.21		$1,360.1048	$1,360.12	$1,360.20	$1,360.10