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	$129.55	7.400%	$139.1367	$139.14	$139.15	$139.10
Purchase #2	$218.70	10.151%	$240.9002	$240.90	$240.90	$240.90
Purchase #3	$45.86	11.242%	$51.0156	$51.02	$51.00	$51.00
Purchase #4	$158.91	7.574%	$170.9458	$170.95	$170.95	$170.90
Purchase #5	$225.94	13.397%	$256.2092	$256.21	$256.20	$256.20
Purchase #6	$182.71	7.311%	$196.0679	$196.07	$196.05	$196.10
Purchase #7	$222.48	9.321%	$243.2174	$243.22	$243.20	$243.20
7 purchase totals =	$1,184.15		$1,297.4928	$1,297.51	$1,297.45	$1,297.40