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	$154.55	3.499%	$159.9577	$159.96	$159.95	$160.00
Purchase #2	$35.40	11.837%	$39.5903	$39.59	$39.60	$39.60
Purchase #3	$208.88	3.105%	$215.3657	$215.37	$215.35	$215.40
Purchase #4	$31.78	4.671%	$33.2644	$33.26	$33.25	$33.30
Purchase #5	$91.89	6.738%	$98.0815	$98.08	$98.10	$98.10
Purchase #6	$209.38	3.291%	$216.2707	$216.27	$216.25	$216.30
Purchase #7	$203.55	9.633%	$223.158	$223.16	$223.15	$223.20
7 purchase totals =	$935.43		$985.6883	$985.69	$985.65	$985.90