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	$101.44	11.229%	$112.8307	$112.83	$112.85	$112.80
Purchase #2	$240.31	13.146%	$271.9012	$271.90	$271.90	$271.90
Purchase #3	$131.70	11.766%	$147.1958	$147.20	$147.20	$147.20
Purchase #4	$71.98	9.675%	$78.9441	$78.94	$78.95	$78.90
Purchase #5	$51.70	3.526%	$53.5229	$53.52	$53.50	$53.50
Purchase #6	$112.78	6.687%	$120.3216	$120.32	$120.30	$120.30
Purchase #7	$12.39	10.780%	$13.7256	$13.73	$13.75	$13.70
7 purchase totals =	$722.30		$798.4419	$798.44	$798.45	$798.30