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	$90.91	9.442%	$99.4937	$99.49	$99.50	$99.50
Purchase #2	$249.62	12.393%	$280.5554	$280.56	$280.55	$280.60
Purchase #3	$163.65	7.251%	$175.5163	$175.52	$175.50	$175.50
Purchase #4	$80.86	11.109%	$89.8427	$89.84	$89.85	$89.80
Purchase #5	$250.83	8.244%	$271.5084	$271.51	$271.50	$271.50
Purchase #6	$210.90	6.425%	$224.4503	$224.45	$224.45	$224.50
Purchase #7	$72.94	5.198%	$76.7314	$76.73	$76.75	$76.70
7 purchase totals =	$1,119.71		$1,218.0982	$1,218.10	$1,218.10	$1,218.10