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	$242.93	6.498%	$258.7156	$258.72	$258.70	$258.70
Purchase #2	$74.81	11.760%	$83.6077	$83.61	$83.60	$83.60
Purchase #3	$123.48	13.847%	$140.5783	$140.58	$140.60	$140.60
Purchase #4	$103.25	9.223%	$112.7727	$112.77	$112.75	$112.80
Purchase #5	$163.95	9.532%	$179.5777	$179.58	$179.60	$179.60
Purchase #6	$92.51	9.399%	$101.205	$101.21	$101.20	$101.20
Purchase #7	$208.84	7.399%	$224.2921	$224.29	$224.30	$224.30
7 purchase totals =	$1,009.77		$1,100.7491	$1,100.76	$1,100.75	$1,100.80