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	$109.89	9.109%	$119.8999	$119.90	$119.90	$119.90
Purchase #2	$146.79	9.362%	$160.5325	$160.53	$160.55	$160.50
Purchase #3	$11.67	12.143%	$13.0871	$13.09	$13.10	$13.10
Purchase #4	$53.88	7.495%	$57.9183	$57.92	$57.90	$57.90
Purchase #5	$192.30	9.847%	$211.2358	$211.24	$211.25	$211.20
Purchase #6	$186.94	5.352%	$196.945	$196.95	$196.95	$196.90
Purchase #7	$107.91	13.444%	$122.4174	$122.42	$122.40	$122.40
7 purchase totals =	$809.38		$882.0360	$882.05	$882.05	$881.90