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	$142.88	11.299%	$159.024	$159.02	$159.00	$159.00
Purchase #2	$222.70	10.202%	$245.4199	$245.42	$245.40	$245.40
Purchase #3	$40.31	4.808%	$42.2481	$42.25	$42.25	$42.20
Purchase #4	$147.83	3.861%	$153.5377	$153.54	$153.55	$153.50
Purchase #5	$154.59	7.735%	$166.5475	$166.55	$166.55	$166.50
Purchase #6	$107.84	13.556%	$122.4588	$122.46	$122.45	$122.50
Purchase #7	$158.76	6.680%	$169.3652	$169.37	$169.35	$169.40
7 purchase totals =	$974.91		$1,058.6012	$1,058.61	$1,058.55	$1,058.50