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	$22.82	5.502%	$24.0756	$24.08	$24.10	$24.10
Purchase #2	$137.85	12.205%	$154.6746	$154.67	$154.65	$154.70
Purchase #3	$187.92	13.299%	$212.9115	$212.91	$212.90	$212.90
Purchase #4	$35.72	13.581%	$40.5711	$40.57	$40.55	$40.60
Purchase #5	$81.57	4.831%	$85.5106	$85.51	$85.50	$85.50
Purchase #6	$56.74	10.433%	$62.6597	$62.66	$62.65	$62.70
Purchase #7	$79.93	11.854%	$89.4049	$89.40	$89.40	$89.40
7 purchase totals =	$602.55		$669.8080	$669.80	$669.75	$669.90