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	$10.67	6.525%	$11.3662	$11.37	$11.35	$11.40
Purchase #2	$227.70	9.712%	$249.8142	$249.81	$249.80	$249.80
Purchase #3	$211.56	6.621%	$225.5674	$225.57	$225.55	$225.60
Purchase #4	$45.49	7.367%	$48.8412	$48.84	$48.85	$48.80
Purchase #5	$137.82	10.205%	$151.8845	$151.88	$151.90	$151.90
Purchase #6	$40.86	3.570%	$42.3187	$42.32	$42.30	$42.30
Purchase #7	$180.51	7.601%	$194.2306	$194.23	$194.25	$194.20
7 purchase totals =	$854.61		$924.0228	$924.02	$924.00	$924.00