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	$23.31	13.362%	$26.4247	$26.42	$26.40	$26.40
Purchase #2	$132.33	9.246%	$144.5652	$144.57	$144.55	$144.60
Purchase #3	$212.74	4.591%	$222.5069	$222.51	$222.50	$222.50
Purchase #4	$50.70	13.359%	$57.473	$57.47	$57.45	$57.50
Purchase #5	$32.41	10.666%	$35.8669	$35.87	$35.85	$35.90
Purchase #6	$42.52	6.389%	$45.2366	$45.24	$45.25	$45.20
Purchase #7	$136.25	6.359%	$144.9141	$144.91	$144.90	$144.90
7 purchase totals =	$630.26		$676.9874	$676.99	$676.90	$677.00