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	$96.62	3.553%	$100.0529	$100.05	$100.05	$100.10
Purchase #2	$238.78	6.565%	$254.4559	$254.46	$254.45	$254.50
Purchase #3	$106.67	9.791%	$117.1141	$117.11	$117.10	$117.10
Purchase #4	$185.41	6.481%	$197.4264	$197.43	$197.45	$197.40
Purchase #5	$66.76	8.654%	$72.5374	$72.54	$72.55	$72.50
Purchase #6	$45.88	9.352%	$50.1707	$50.17	$50.15	$50.20
Purchase #7	$48.69	5.533%	$51.384	$51.38	$51.40	$51.40
7 purchase totals =	$788.81		$843.1414	$843.14	$843.15	$843.20