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	$50.30	7.800%	$54.2234	$54.22	$54.20	$54.20
Purchase #2	$141.86	6.703%	$151.3689	$151.37	$151.35	$151.40
Purchase #3	$180.80	8.706%	$196.5404	$196.54	$196.55	$196.50
Purchase #4	$108.99	10.311%	$120.228	$120.23	$120.25	$120.20
Purchase #5	$104.44	9.361%	$114.2166	$114.22	$114.20	$114.20
Purchase #6	$100.75	11.304%	$112.1388	$112.14	$112.15	$112.10
Purchase #7	$26.25	11.669%	$29.3131	$29.31	$29.30	$29.30
7 purchase totals =	$713.39		$778.0292	$778.03	$778.00	$777.90