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	$205.57	12.655%	$231.5849	$231.58	$231.60	$231.60
Purchase #2	$87.68	13.497%	$99.5142	$99.51	$99.50	$99.50
Purchase #3	$50.43	13.139%	$57.056	$57.06	$57.05	$57.10
Purchase #4	$72.25	9.245%	$78.9295	$78.93	$78.95	$78.90
Purchase #5	$98.43	8.231%	$106.5318	$106.53	$106.55	$106.50
Purchase #6	$170.73	3.839%	$177.2843	$177.28	$177.30	$177.30
Purchase #7	$39.71	9.219%	$43.3709	$43.37	$43.35	$43.40
7 purchase totals =	$724.80		$794.2716	$794.26	$794.30	$794.30