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	$78.88	13.822%	$89.7828	$89.78	$89.80	$89.80
Purchase #2	$40.66	7.819%	$43.8392	$43.84	$43.85	$43.80
Purchase #3	$187.78	11.337%	$209.0686	$209.07	$209.05	$209.10
Purchase #4	$10.89	7.755%	$11.7345	$11.73	$11.75	$11.70
Purchase #5	$62.52	3.272%	$64.5657	$64.57	$64.55	$64.60
Purchase #6	$132.32	12.463%	$148.811	$148.81	$148.80	$148.80
Purchase #7	$107.81	3.424%	$111.5014	$111.50	$111.50	$111.50
7 purchase totals =	$620.86		$679.3032	$679.30	$679.30	$679.30