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	$235.80	9.367%	$257.8874	$257.89	$257.90	$257.90
Purchase #2	$208.56	6.396%	$221.8995	$221.90	$221.90	$221.90
Purchase #3	$238.85	10.770%	$264.5741	$264.57	$264.55	$264.60
Purchase #4	$73.43	12.303%	$82.4641	$82.46	$82.45	$82.50
Purchase #5	$23.61	7.552%	$25.393	$25.39	$25.40	$25.40
Purchase #6	$191.50	12.231%	$214.9224	$214.92	$214.90	$214.90
Purchase #7	$51.47	9.874%	$56.5521	$56.55	$56.55	$56.60
7 purchase totals =	$1,023.22		$1,123.6926	$1,123.68	$1,123.65	$1,123.80