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	$19.72	3.308%	$20.3723	$20.37	$20.35	$20.40
Purchase #2	$120.40	5.683%	$127.2423	$127.24	$127.25	$127.20
Purchase #3	$229.70	8.871%	$250.0767	$250.08	$250.10	$250.10
Purchase #4	$68.88	3.710%	$71.4354	$71.44	$71.45	$71.40
Purchase #5	$110.81	10.668%	$122.6312	$122.63	$122.65	$122.60
Purchase #6	$206.63	10.589%	$228.5101	$228.51	$228.50	$228.50
Purchase #7	$180.40	10.647%	$199.6072	$199.61	$199.60	$199.60
7 purchase totals =	$936.54		$1,019.8752	$1,019.88	$1,019.90	$1,019.80