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	$29.25	10.311%	$32.266	$32.27	$32.25	$32.30
Purchase #2	$27.59	10.832%	$30.5785	$30.58	$30.60	$30.60
Purchase #3	$147.94	4.607%	$154.7556	$154.76	$154.75	$154.80
Purchase #4	$171.48	11.655%	$191.466	$191.47	$191.45	$191.50
Purchase #5	$134.85	3.279%	$139.2717	$139.27	$139.25	$139.30
Purchase #6	$59.97	4.287%	$62.5409	$62.54	$62.55	$62.50
Purchase #7	$71.48	10.277%	$78.826	$78.83	$78.85	$78.80
7 purchase totals =	$642.56		$689.7047	$689.72	$689.70	$689.80