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	$45.25	11.873%	$50.6225	$50.62	$50.60	$50.60
Purchase #2	$36.43	12.233%	$40.8865	$40.89	$40.90	$40.90
Purchase #3	$216.86	9.760%	$238.0255	$238.03	$238.05	$238.00
Purchase #4	$194.44	7.546%	$209.1124	$209.11	$209.10	$209.10
Purchase #5	$168.48	11.683%	$188.1635	$188.16	$188.15	$188.20
Purchase #6	$39.44	12.346%	$44.3093	$44.31	$44.30	$44.30
Purchase #7	$185.91	13.589%	$211.1733	$211.17	$211.15	$211.20
7 purchase totals =	$886.81		$982.2930	$982.29	$982.25	$982.30