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	$67.75	11.431%	$75.4945	$75.49	$75.50	$75.50
Purchase #2	$71.52	9.782%	$78.5161	$78.52	$78.50	$78.50
Purchase #3	$116.87	5.646%	$123.4685	$123.47	$123.45	$123.50
Purchase #4	$191.40	6.385%	$203.6209	$203.62	$203.60	$203.60
Purchase #5	$140.69	11.161%	$156.3924	$156.39	$156.40	$156.40
Purchase #6	$136.92	6.181%	$145.383	$145.38	$145.40	$145.40
Purchase #7	$124.56	12.449%	$140.0665	$140.07	$140.05	$140.10
7 purchase totals =	$849.71		$922.9419	$922.94	$922.90	$923.00