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	$6.83	12.620%	$7.6919	$7.69	$7.70	$7.70
Purchase #2	$174.33	9.531%	$190.9454	$190.95	$190.95	$190.90
Purchase #3	$164.80	6.375%	$175.306	$175.31	$175.30	$175.30
Purchase #4	$158.32	8.777%	$172.2157	$172.22	$172.20	$172.20
Purchase #5	$171.28	9.801%	$188.0672	$188.07	$188.05	$188.10
Purchase #6	$57.26	8.462%	$62.1053	$62.11	$62.10	$62.10
Purchase #7	$184.64	12.781%	$208.2388	$208.24	$208.25	$208.20
7 purchase totals =	$917.46		$1,004.5703	$1,004.59	$1,004.55	$1,004.50