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	$59.83	12.818%	$67.499	$67.50	$67.50	$67.50
Purchase #2	$58.93	6.189%	$62.5772	$62.58	$62.60	$62.60
Purchase #3	$61.75	12.185%	$69.2742	$69.27	$69.25	$69.30
Purchase #4	$166.31	7.685%	$179.0909	$179.09	$179.10	$179.10
Purchase #5	$119.45	6.415%	$127.1127	$127.11	$127.10	$127.10
Purchase #6	$63.48	3.342%	$65.6015	$65.60	$65.60	$65.60
Purchase #7	$189.75	12.423%	$213.3226	$213.32	$213.30	$213.30
7 purchase totals =	$719.50		$784.4781	$784.47	$784.45	$784.50