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	$136.48	13.801%	$155.3156	$155.32	$155.30	$155.30
Purchase #2	$235.53	9.779%	$258.5625	$258.56	$258.55	$258.60
Purchase #3	$123.27	4.485%	$128.7987	$128.80	$128.80	$128.80
Purchase #4	$95.80	4.224%	$99.8466	$99.85	$99.85	$99.80
Purchase #5	$44.58	3.311%	$46.056	$46.06	$46.05	$46.10
Purchase #6	$55.68	7.695%	$59.9646	$59.96	$59.95	$60.00
Purchase #7	$61.25	7.696%	$65.9638	$65.96	$65.95	$66.00
7 purchase totals =	$752.59		$814.5078	$814.51	$814.45	$814.60