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	$133.70	3.600%	$138.5132	$138.51	$138.50	$138.50
Purchase #2	$156.75	12.443%	$176.2544	$176.25	$176.25	$176.30
Purchase #3	$222.56	5.478%	$234.7518	$234.75	$234.75	$234.80
Purchase #4	$99.77	13.633%	$113.3716	$113.37	$113.35	$113.40
Purchase #5	$80.59	11.362%	$89.7466	$89.75	$89.75	$89.70
Purchase #6	$79.32	13.608%	$90.1139	$90.11	$90.10	$90.10
Purchase #7	$172.28	8.653%	$187.1874	$187.19	$187.20	$187.20
7 purchase totals =	$944.97		$1,029.9389	$1,029.93	$1,029.90	$1,030.00