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	$239.30	7.505%	$257.2595	$257.26	$257.25	$257.30
Purchase #2	$85.58	13.220%	$96.8937	$96.89	$96.90	$96.90
Purchase #3	$168.32	13.427%	$190.9203	$190.92	$190.90	$190.90
Purchase #4	$73.51	6.195%	$78.0639	$78.06	$78.05	$78.10
Purchase #5	$127.89	11.180%	$142.1881	$142.19	$142.20	$142.20
Purchase #6	$243.88	11.574%	$272.1067	$272.11	$272.10	$272.10
Purchase #7	$13.99	10.425%	$15.4485	$15.45	$15.45	$15.40
7 purchase totals =	$952.47		$1,052.8807	$1,052.88	$1,052.85	$1,052.90