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	$132.89	6.212%	$141.1451	$141.15	$141.15	$141.10
Purchase #2	$80.96	12.238%	$90.8679	$90.87	$90.85	$90.90
Purchase #3	$147.53	13.516%	$167.4702	$167.47	$167.45	$167.50
Purchase #4	$90.66	4.144%	$94.417	$94.42	$94.40	$94.40
Purchase #5	$12.99	8.393%	$14.0803	$14.08	$14.10	$14.10
Purchase #6	$58.95	12.497%	$66.317	$66.32	$66.30	$66.30
Purchase #7	$166.64	5.303%	$175.4769	$175.48	$175.50	$175.50
7 purchase totals =	$690.62		$749.7744	$749.79	$749.75	$749.80