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	$72.72	6.869%	$77.7151	$77.72	$77.70	$77.70
Purchase #2	$192.95	13.161%	$218.3441	$218.34	$218.35	$218.30
Purchase #3	$96.47	9.139%	$105.2864	$105.29	$105.30	$105.30
Purchase #4	$160.72	11.470%	$179.1546	$179.15	$179.15	$179.20
Purchase #5	$73.67	9.391%	$80.5883	$80.59	$80.60	$80.60
Purchase #6	$145.29	9.497%	$159.0882	$159.09	$159.10	$159.10
Purchase #7	$41.51	5.207%	$43.6714	$43.67	$43.65	$43.70
7 purchase totals =	$783.33		$863.8481	$863.85	$863.85	$863.90