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	$78.82	13.484%	$89.4481	$89.45	$89.45	$89.40
Purchase #2	$38.46	12.135%	$43.1271	$43.13	$43.15	$43.10
Purchase #3	$110.60	3.401%	$114.3615	$114.36	$114.35	$114.40
Purchase #4	$70.26	9.539%	$76.9621	$76.96	$76.95	$77.00
Purchase #5	$25.79	4.865%	$27.0447	$27.04	$27.05	$27.00
Purchase #6	$148.77	4.761%	$155.8529	$155.85	$155.85	$155.90
Purchase #7	$91.62	7.264%	$98.2753	$98.28	$98.30	$98.30
7 purchase totals =	$564.32		$605.0717	$605.07	$605.10	$605.10