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	$12.44	3.665%	$12.8959	$12.90	$12.90	$12.90
Purchase #2	$95.26	3.820%	$98.8989	$98.90	$98.90	$98.90
Purchase #3	$226.52	12.722%	$255.3379	$255.34	$255.35	$255.30
Purchase #4	$116.65	6.125%	$123.7948	$123.79	$123.80	$123.80
Purchase #5	$122.80	12.744%	$138.4496	$138.45	$138.45	$138.40
Purchase #6	$69.32	13.524%	$78.6948	$78.69	$78.70	$78.70
Purchase #7	$34.53	3.299%	$35.6691	$35.67	$35.65	$35.70
7 purchase totals =	$677.52		$743.7410	$743.74	$743.75	$743.70