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	$76.31	7.819%	$82.2767	$82.28	$82.30	$82.30
Purchase #2	$241.96	7.537%	$260.1965	$260.20	$260.20	$260.20
Purchase #3	$95.89	13.135%	$108.4852	$108.49	$108.50	$108.50
Purchase #4	$93.70	5.216%	$98.5874	$98.59	$98.60	$98.60
Purchase #5	$39.66	9.838%	$43.5618	$43.56	$43.55	$43.60
Purchase #6	$127.66	3.338%	$131.9213	$131.92	$131.90	$131.90
Purchase #7	$224.59	13.871%	$255.7429	$255.74	$255.75	$255.70
7 purchase totals =	$899.77		$980.7718	$980.78	$980.80	$980.80