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	$233.93	9.708%	$256.6399	$256.64	$256.65	$256.60
Purchase #2	$148.50	11.278%	$165.2478	$165.25	$165.25	$165.20
Purchase #3	$134.45	5.421%	$141.7385	$141.74	$141.75	$141.70
Purchase #4	$33.54	6.181%	$35.6131	$35.61	$35.60	$35.60
Purchase #5	$38.89	12.320%	$43.6812	$43.68	$43.70	$43.70
Purchase #6	$234.67	4.707%	$245.7159	$245.72	$245.70	$245.70
Purchase #7	$48.76	7.207%	$52.2741	$52.27	$52.25	$52.30
7 purchase totals =	$872.74		$940.9105	$940.91	$940.90	$940.80