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	$108.91	13.784%	$123.9222	$123.92	$123.90	$123.90
Purchase #2	$150.83	9.636%	$165.364	$165.36	$165.35	$165.40
Purchase #3	$56.47	9.110%	$61.6144	$61.61	$61.60	$61.60
Purchase #4	$233.45	13.588%	$265.1712	$265.17	$265.15	$265.20
Purchase #5	$218.73	3.644%	$226.7005	$226.70	$226.70	$226.70
Purchase #6	$42.71	3.630%	$44.2604	$44.26	$44.25	$44.30
Purchase #7	$186.47	5.624%	$196.9571	$196.96	$196.95	$197.00
7 purchase totals =	$997.57		$1,083.9898	$1,083.98	$1,083.90	$1,084.10