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	$6.46	6.253%	$6.8639	$6.86	$6.85	$6.90
Purchase #2	$100.33	7.370%	$107.7243	$107.72	$107.70	$107.70
Purchase #3	$81.85	9.116%	$89.3114	$89.31	$89.30	$89.30
Purchase #4	$196.59	4.529%	$205.4936	$205.49	$205.50	$205.50
Purchase #5	$18.98	7.377%	$20.3802	$20.38	$20.40	$20.40
Purchase #6	$42.71	9.871%	$46.9259	$46.93	$46.95	$46.90
Purchase #7	$43.53	7.117%	$46.628	$46.63	$46.65	$46.60
7 purchase totals =	$490.45		$523.3273	$523.32	$523.35	$523.30