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	$73.87	6.326%	$78.543	$78.54	$78.55	$78.50
Purchase #2	$162.92	13.734%	$185.2954	$185.30	$185.30	$185.30
Purchase #3	$96.80	8.547%	$105.0735	$105.07	$105.05	$105.10
Purchase #4	$81.57	10.665%	$90.2694	$90.27	$90.25	$90.30
Purchase #5	$37.51	12.787%	$42.3064	$42.31	$42.30	$42.30
Purchase #6	$140.69	11.190%	$156.4332	$156.43	$156.45	$156.40
Purchase #7	$130.78	5.669%	$138.1939	$138.19	$138.20	$138.20
7 purchase totals =	$724.14		$796.1148	$796.11	$796.10	$796.10