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	$5.51	10.370%	$6.0814	$6.08	$6.10	$6.10
Purchase #2	$171.32	13.280%	$194.0713	$194.07	$194.05	$194.10
Purchase #3	$249.39	8.618%	$270.8824	$270.88	$270.90	$270.90
Purchase #4	$114.88	10.807%	$127.2951	$127.30	$127.30	$127.30
Purchase #5	$160.54	12.430%	$180.4951	$180.50	$180.50	$180.50
Purchase #6	$202.54	9.224%	$221.2223	$221.22	$221.20	$221.20
Purchase #7	$77.83	10.431%	$85.9484	$85.95	$85.95	$85.90
7 purchase totals =	$982.01		$1,085.9960	$1,086.00	$1,086.00	$1,086.00