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	$37.48	13.489%	$42.5357	$42.54	$42.55	$42.50
Purchase #2	$239.44	3.772%	$248.4717	$248.47	$248.45	$248.50
Purchase #3	$214.50	7.336%	$230.2357	$230.24	$230.25	$230.20
Purchase #4	$149.79	11.718%	$167.3424	$167.34	$167.35	$167.30
Purchase #5	$118.72	10.754%	$131.4871	$131.49	$131.50	$131.50
Purchase #6	$81.35	8.788%	$88.499	$88.50	$88.50	$88.50
Purchase #7	$83.43	3.204%	$86.1031	$86.10	$86.10	$86.10
7 purchase totals =	$924.71		$994.6747	$994.68	$994.70	$994.60