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	$125.63	13.851%	$143.031	$143.03	$143.05	$143.00
Purchase #2	$147.63	11.321%	$164.3432	$164.34	$164.35	$164.30
Purchase #3	$250.44	7.566%	$269.3883	$269.39	$269.40	$269.40
Purchase #4	$28.85	9.355%	$31.5489	$31.55	$31.55	$31.50
Purchase #5	$126.46	13.572%	$143.6232	$143.62	$143.60	$143.60
Purchase #6	$232.62	7.423%	$249.8874	$249.89	$249.90	$249.90
Purchase #7	$250.38	11.373%	$278.8557	$278.86	$278.85	$278.90
7 purchase totals =	$1,162.01		$1,280.6777	$1,280.68	$1,280.70	$1,280.60