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	$229.93	11.425%	$256.1995	$256.20	$256.20	$256.20
Purchase #2	$78.42	8.757%	$85.2872	$85.29	$85.30	$85.30
Purchase #3	$135.78	7.436%	$145.8766	$145.88	$145.90	$145.90
Purchase #4	$68.46	7.737%	$73.7568	$73.76	$73.75	$73.80
Purchase #5	$74.34	5.765%	$78.6257	$78.63	$78.65	$78.60
Purchase #6	$146.86	3.286%	$151.6858	$151.69	$151.70	$151.70
Purchase #7	$87.58	11.781%	$97.8978	$97.90	$97.90	$97.90
7 purchase totals =	$821.37		$889.3294	$889.35	$889.40	$889.40