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	$109.98	13.294%	$124.6007	$124.60	$124.60	$124.60
Purchase #2	$198.75	12.395%	$223.3851	$223.39	$223.40	$223.40
Purchase #3	$175.71	11.626%	$196.138	$196.14	$196.15	$196.10
Purchase #4	$147.44	4.338%	$153.8359	$153.84	$153.85	$153.80
Purchase #5	$30.68	4.818%	$32.1582	$32.16	$32.15	$32.20
Purchase #6	$230.49	12.450%	$259.186	$259.19	$259.20	$259.20
Purchase #7	$54.72	8.263%	$59.2415	$59.24	$59.25	$59.20
7 purchase totals =	$947.77		$1,048.5454	$1,048.56	$1,048.60	$1,048.50