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	$88.55	12.457%	$99.5807	$99.58	$99.60	$99.60
Purchase #2	$94.50	7.833%	$101.9022	$101.90	$101.90	$101.90
Purchase #3	$249.64	5.458%	$263.2654	$263.27	$263.25	$263.30
Purchase #4	$47.93	5.411%	$50.5235	$50.52	$50.50	$50.50
Purchase #5	$170.73	12.689%	$192.3939	$192.39	$192.40	$192.40
Purchase #6	$56.71	10.800%	$62.8347	$62.83	$62.85	$62.80
Purchase #7	$196.58	9.792%	$215.8291	$215.83	$215.85	$215.80
7 purchase totals =	$904.64		$986.3295	$986.32	$986.35	$986.30