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	$89.69	12.370%	$100.7847	$100.78	$100.80	$100.80
Purchase #2	$237.83	7.448%	$255.5436	$255.54	$255.55	$255.50
Purchase #3	$151.84	6.490%	$161.6944	$161.69	$161.70	$161.70
Purchase #4	$101.48	8.238%	$109.8399	$109.84	$109.85	$109.80
Purchase #5	$247.72	6.628%	$264.1389	$264.14	$264.15	$264.10
Purchase #6	$52.61	11.824%	$58.8306	$58.83	$58.85	$58.80
Purchase #7	$138.48	7.519%	$148.8923	$148.89	$148.90	$148.90
7 purchase totals =	$1,019.65		$1,099.7244	$1,099.71	$1,099.80	$1,099.60