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	$73.51	6.739%	$78.4638	$78.46	$78.45	$78.50
Purchase #2	$169.67	6.860%	$181.3094	$181.31	$181.30	$181.30
Purchase #3	$106.83	6.689%	$113.9759	$113.98	$114.00	$114.00
Purchase #4	$124.39	4.183%	$129.5932	$129.59	$129.60	$129.60
Purchase #5	$242.79	11.151%	$269.8635	$269.86	$269.85	$269.90
Purchase #6	$47.80	10.753%	$52.9399	$52.94	$52.95	$52.90
Purchase #7	$56.44	10.389%	$62.3036	$62.30	$62.30	$62.30
7 purchase totals =	$821.43		$888.4493	$888.44	$888.45	$888.50