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	$243.48	6.346%	$258.9312	$258.93	$258.95	$258.90
Purchase #2	$164.31	13.506%	$186.5017	$186.50	$186.50	$186.50
Purchase #3	$220.63	11.356%	$245.6847	$245.68	$245.70	$245.70
Purchase #4	$89.73	11.874%	$100.3845	$100.38	$100.40	$100.40
Purchase #5	$103.56	12.224%	$116.2192	$116.22	$116.20	$116.20
Purchase #6	$139.54	5.682%	$147.4687	$147.47	$147.45	$147.50
Purchase #7	$14.91	9.714%	$16.3584	$16.36	$16.35	$16.40
7 purchase totals =	$976.16		$1,071.5484	$1,071.54	$1,071.55	$1,071.60