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	$94.47	9.457%	$103.404	$103.40	$103.40	$103.40
Purchase #2	$54.93	13.507%	$62.3494	$62.35	$62.35	$62.30
Purchase #3	$94.36	11.859%	$105.5502	$105.55	$105.55	$105.60
Purchase #4	$57.32	4.826%	$60.0863	$60.09	$60.10	$60.10
Purchase #5	$161.25	4.499%	$168.5046	$168.50	$168.50	$168.50
Purchase #6	$36.61	11.751%	$40.912	$40.91	$40.90	$40.90
Purchase #7	$93.29	11.136%	$103.6788	$103.68	$103.70	$103.70
7 purchase totals =	$592.23		$644.4853	$644.48	$644.50	$644.50