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	$80.76	7.820%	$87.0754	$87.08	$87.10	$87.10
Purchase #2	$173.78	5.240%	$182.8861	$182.89	$182.90	$182.90
Purchase #3	$136.51	7.733%	$147.0663	$147.07	$147.05	$147.10
Purchase #4	$47.30	3.374%	$48.8959	$48.90	$48.90	$48.90
Purchase #5	$57.92	9.651%	$63.5099	$63.51	$63.50	$63.50
Purchase #6	$80.89	12.364%	$90.8912	$90.89	$90.90	$90.90
Purchase #7	$208.57	12.838%	$235.3462	$235.35	$235.35	$235.30
7 purchase totals =	$785.73		$855.6710	$855.69	$855.70	$855.70