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	$78.44	4.345%	$81.8482	$81.85	$81.85	$81.80
Purchase #2	$84.26	13.711%	$95.8129	$95.81	$95.80	$95.80
Purchase #3	$225.70	3.605%	$233.8365	$233.84	$233.85	$233.80
Purchase #4	$208.50	8.805%	$226.8584	$226.86	$226.85	$226.90
Purchase #5	$54.47	10.354%	$60.1098	$60.11	$60.10	$60.10
Purchase #6	$79.95	11.735%	$89.3321	$89.33	$89.35	$89.30
Purchase #7	$177.36	7.465%	$190.5999	$190.60	$190.60	$190.60
7 purchase totals =	$908.68		$978.3978	$978.40	$978.40	$978.30