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	$77.28	9.365%	$84.5173	$84.52	$84.50	$84.50
Purchase #2	$99.82	9.597%	$109.3997	$109.40	$109.40	$109.40
Purchase #3	$227.56	5.844%	$240.8586	$240.86	$240.85	$240.90
Purchase #4	$6.54	7.109%	$7.0049	$7.00	$7.00	$7.00
Purchase #5	$101.63	12.240%	$114.0695	$114.07	$114.05	$114.10
Purchase #6	$92.59	4.239%	$96.5149	$96.51	$96.50	$96.50
Purchase #7	$80.70	11.456%	$89.945	$89.95	$89.95	$89.90
7 purchase totals =	$686.12		$742.3099	$742.31	$742.25	$742.30