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	$239.48	4.493%	$250.2398	$250.24	$250.25	$250.20
Purchase #2	$146.62	6.682%	$156.4171	$156.42	$156.40	$156.40
Purchase #3	$91.91	12.103%	$103.0339	$103.03	$103.05	$103.00
Purchase #4	$219.58	4.174%	$228.7453	$228.75	$228.75	$228.70
Purchase #5	$213.96	11.262%	$238.0562	$238.06	$238.05	$238.10
Purchase #6	$37.59	7.676%	$40.4754	$40.48	$40.50	$40.50
Purchase #7	$28.91	11.664%	$32.2821	$32.28	$32.30	$32.30
7 purchase totals =	$978.05		$1,049.2498	$1,049.26	$1,049.30	$1,049.20