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	$178.43	4.314%	$186.1275	$186.13	$186.15	$186.10
Purchase #2	$152.67	12.330%	$171.4942	$171.49	$171.50	$171.50
Purchase #3	$228.69	9.808%	$251.1199	$251.12	$251.10	$251.10
Purchase #4	$119.97	9.590%	$131.4751	$131.48	$131.50	$131.50
Purchase #5	$36.33	11.747%	$40.5977	$40.60	$40.60	$40.60
Purchase #6	$246.55	3.588%	$255.3962	$255.40	$255.40	$255.40
Purchase #7	$132.49	9.484%	$145.0554	$145.06	$145.05	$145.10
7 purchase totals =	$1,095.13		$1,181.2660	$1,181.28	$1,181.30	$1,181.30