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	$78.31	13.701%	$89.0393	$89.04	$89.05	$89.00
Purchase #2	$17.71	12.400%	$19.906	$19.91	$19.90	$19.90
Purchase #3	$116.48	13.661%	$132.3923	$132.39	$132.40	$132.40
Purchase #4	$83.28	3.617%	$86.2922	$86.29	$86.30	$86.30
Purchase #5	$99.65	10.752%	$110.3644	$110.36	$110.35	$110.40
Purchase #6	$203.36	13.526%	$230.8665	$230.87	$230.85	$230.90
Purchase #7	$103.89	7.145%	$111.3129	$111.31	$111.30	$111.30
7 purchase totals =	$702.68		$780.1736	$780.17	$780.15	$780.20