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	$226.30	5.429%	$238.5858	$238.59	$238.60	$238.60
Purchase #2	$248.61	9.748%	$272.8445	$272.84	$272.85	$272.80
Purchase #3	$135.43	12.605%	$152.501	$152.50	$152.50	$152.50
Purchase #4	$88.93	11.740%	$99.3704	$99.37	$99.35	$99.40
Purchase #5	$134.85	9.174%	$147.2211	$147.22	$147.20	$147.20
Purchase #6	$209.43	13.292%	$237.2674	$237.27	$237.25	$237.30
Purchase #7	$59.69	13.815%	$67.9362	$67.94	$67.95	$67.90
7 purchase totals =	$1,103.24		$1,215.7264	$1,215.73	$1,215.70	$1,215.70