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	$39.43	8.794%	$42.8975	$42.90	$42.90	$42.90
Purchase #2	$83.58	8.171%	$90.4093	$90.41	$90.40	$90.40
Purchase #3	$97.90	6.251%	$104.0197	$104.02	$104.00	$104.00
Purchase #4	$242.71	13.187%	$274.7162	$274.72	$274.70	$274.70
Purchase #5	$109.40	4.178%	$113.9707	$113.97	$113.95	$114.00
Purchase #6	$131.52	9.301%	$143.7527	$143.75	$143.75	$143.80
Purchase #7	$6.36	11.407%	$7.0855	$7.09	$7.10	$7.10
7 purchase totals =	$710.90		$776.8516	$776.86	$776.80	$776.90