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	$37.49	13.872%	$42.6906	$42.69	$42.70	$42.70
Purchase #2	$125.54	9.783%	$137.8216	$137.82	$137.80	$137.80
Purchase #3	$154.96	11.695%	$173.0826	$173.08	$173.10	$173.10
Purchase #4	$97.82	11.638%	$109.2043	$109.20	$109.20	$109.20
Purchase #5	$226.34	12.699%	$255.0829	$255.08	$255.10	$255.10
Purchase #6	$79.31	9.405%	$86.7691	$86.77	$86.75	$86.80
Purchase #7	$242.50	10.836%	$268.7773	$268.78	$268.80	$268.80
7 purchase totals =	$963.96		$1,073.4284	$1,073.42	$1,073.45	$1,073.50