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	$93.78	7.494%	$100.8079	$100.81	$100.80	$100.80
Purchase #2	$180.98	3.290%	$186.9342	$186.93	$186.95	$186.90
Purchase #3	$130.98	6.794%	$139.8788	$139.88	$139.90	$139.90
Purchase #4	$14.43	8.167%	$15.6085	$15.61	$15.60	$15.60
Purchase #5	$219.65	10.701%	$243.1547	$243.15	$243.15	$243.20
Purchase #6	$137.53	5.467%	$145.0488	$145.05	$145.05	$145.00
Purchase #7	$43.89	7.399%	$47.1374	$47.14	$47.15	$47.10
7 purchase totals =	$821.24		$878.5703	$878.57	$878.60	$878.50