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	$53.54	9.555%	$58.6557	$58.66	$58.65	$58.70
Purchase #2	$147.30	13.691%	$167.4668	$167.47	$167.45	$167.50
Purchase #3	$137.61	5.206%	$144.774	$144.77	$144.75	$144.80
Purchase #4	$9.62	8.510%	$10.4387	$10.44	$10.45	$10.40
Purchase #5	$223.96	6.622%	$238.7906	$238.79	$238.80	$238.80
Purchase #6	$69.66	13.242%	$78.8844	$78.88	$78.90	$78.90
Purchase #7	$159.91	7.134%	$171.318	$171.32	$171.30	$171.30
7 purchase totals =	$801.60		$870.3282	$870.33	$870.30	$870.40