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	$127.38	9.607%	$139.6174	$139.62	$139.60	$139.60
Purchase #2	$91.52	6.330%	$97.3132	$97.31	$97.30	$97.30
Purchase #3	$51.80	7.607%	$55.7404	$55.74	$55.75	$55.70
Purchase #4	$99.40	9.253%	$108.5975	$108.60	$108.60	$108.60
Purchase #5	$55.68	6.770%	$59.4495	$59.45	$59.45	$59.40
Purchase #6	$132.53	3.177%	$136.7405	$136.74	$136.75	$136.70
Purchase #7	$215.85	3.332%	$223.0421	$223.04	$223.05	$223.00
7 purchase totals =	$774.16		$820.5006	$820.50	$820.50	$820.30