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	$225.67	3.345%	$233.2187	$233.22	$233.20	$233.20
Purchase #2	$154.65	6.637%	$164.9141	$164.91	$164.90	$164.90
Purchase #3	$202.43	12.714%	$228.167	$228.17	$228.15	$228.20
Purchase #4	$22.43	4.516%	$23.4429	$23.44	$23.45	$23.40
Purchase #5	$93.69	7.744%	$100.9454	$100.95	$100.95	$100.90
Purchase #6	$55.66	7.143%	$59.6358	$59.64	$59.65	$59.60
Purchase #7	$9.69	12.214%	$10.8735	$10.87	$10.85	$10.90
7 purchase totals =	$764.22		$821.1974	$821.20	$821.15	$821.10